共查询到20条相似文献，搜索用时 15 毫秒
1.
生态城市与城市绿化 总被引：22，自引：0，他引：22
良好地反映人与自然和谐发展关系 ,各项规划建设能以不使环境遭到破坏为标准 ,行为主体的活动能自觉地朝利于维护周围环境并融于自然的天然群落即为生态城市。城市绿化的作用在于改善气候、改善环境卫生、蓄水防洪、防灾减灾、美化环境、节约能源等。目前在我国城市绿化方面存在着以下问题 :①都市规划缺乏宏观性、全面性和远见性 ;②绿色城市观念没有在大多数市民中形成 ;③缺乏硬性绿化指标 ;④绿化模式脱离国情、市情 ;⑤园林水平与国外相比有较大差距 ;⑥修建大草坪热温度居高不下 ;⑦城市绿化简单化 ;⑧应该绿化可以绿化的地方尚未绿化 ;⑨绿化布局、比例不尽合理与和谐 ;⑩重种植轻管护。针对以上问题 ,提出了创建生态城市的建议 相似文献
2.
Effects of relative shoot height and irradiance on shoot and leaf properties of Quercus serrata Thunb. saplings growing in the understory and in gaps were investigated. Photosynthetic photon flux (PPF) at the location of the shoot relative to that in the open (relative PPF; rPPF) and the height of the shoot base relative to tree height (relative height; rHeight) were measured for all current-year shoots of each sapling. Current-year shoot properties (length, leaf area, number of daughter shoots) and mortality, and leaf properties (mass per area (LMA) and nitrogen content per area (N(area))) were examined in relation to rPPF and rHeight. N(area) was used as a proxy for area-based assimilative capacity. Shoot length, leaf area per shoot and number of daughter shoots increased with increasing rHeight, especially in well-lit conditions. Shoot mortality decreased with increasing rHeight and rPPF. Both LMA and N(area) were positively correlated with rPPF, but not rHeight. 相似文献
3.
异长叶烯基噻唑类化合物的合成及其抑菌、抗肿瘤活性研究 总被引：1，自引：0，他引：1
以异长烯酮为原料,通过缩合、亲核取代和环化等手段合成了11种新型异长叶烯基噻唑类化合物,同时采用1H NMR、13C NMR、LC-MS和FT-IR对化合物进行了鉴定,从而确定了化合物的结构。对目标化合物进行了抑菌活性实验,结果表明:(E)-4-(4-甲氧基苯基)-2-(2-(1,1,5,5-四甲基-3,4,5,6-四氢-1H-2,4a-亚甲基-7(2H)-亚基)肼基)噻唑(2e)与(E)-4-(4-甲基苯基)-2-(2-(1,1,5,5-四甲基-3,4,5,6-四氢-1H-2,4a-亚甲基-7(2H)-亚基)肼基)噻唑(2g)对细菌(大肠杆菌与金黄色葡萄球菌)具有较好的抑制效果,最低抑菌质量浓度(MIC)为7.8 mg/L。(E)-4-氯苯基-2-(2-(1,1,5,5-四甲基-3,4,5,6-四氢-1H-2,4a-亚甲基-7(2H)-亚基)肼基)噻唑(2b)对真菌(白念球菌与热带假丝酵母)抑制效果优于其他化合物,其MIC值为15.6 mg/L。采用噻唑蓝(MTT)法对目标化合物进行了人体肝癌细胞(HepG 2)抗癌活性测试,化合物2g(IC50=43.9±0.9 mg/L)对HepG 2具有较好的抗癌活性。 相似文献
4.
世界毁林趋势及其原因和后果 总被引：1，自引：0，他引：1
全球森林每年消毁达1100万公顷,主要是发展中国家的热带森林,温带森林变化不大,有些国家还有所增加。但面临着酸雨的危害,造成部分地区森林片状衰亡。森林消毁的原因是:(1)滥伐而不更新;(2)砍伐森林转为农业用地或牧场;(3)砍伐大量燃料用材。森林大幅度消减后所带来的后果;(1)影响气候变化,使全球性水文循环失调,改变了大气的组成,增加大气中二氧化碳含量,造成增温;(2)加剧水源区土壤侵蚀,造成河流下游泥沙淤积;(3)不少动植物物种濒临灭绝。 相似文献
5.
Jack pine (Pinus banksiana Lamb.) seedlings were grown in a shaded or unshaded light regime with either NO(3) (-)- or NH(4) (+)-N as the sole N source. After three months, seedlings grown with NH(4) (+)-N were larger than seedlings grown with NO(3) (-)-N. Irradiance had a greater effect on growth of ammonium-fed seedlings than on growth of nitrate-fed seedlings.At all times from 6 to 24 h following incorporation of (15)N, soluble, insoluble, and total (15)N contents of shoots and roots were higher in ammonium-fed seedlings than in nitrate-fed seedlings. The pattern of (15)N accumulation in shoots was similar to that in roots. After 6 and 24 h of (15)N incorporation, unshaded, ammonium-fed seedlings had 8.8 and 2.8 times greater total (15)N contents, respectively, than unshaded, nitrate-fed seedlings. In response to shading, ammonium-fed seedlings increased their total uptake of (15)N per unit root weight, whereas nitrate-fed seedlings did not. No nitrate or (15)NO(3) (-) was detected in any plant tissue. Nitrate-fed plants had higher NH(4) (+), Asp, and Gln concentrations in needles and higher gamma-aminobutyric acid and Arg concentrations in stems. Accumulation of (15)N in roots was not affected by the pH of the (15)N solution or by the N source fed to the seedlings before the period of (15)N incorporation. Thus NO(3) (-) transport into roots, rather than its reduction or transport within the plant, seems to be the factor limiting the growth of jack pine supplied with NO(3) (-)-N as the sole N source. 相似文献
6.
Rodríguez-Calcerrada J Limousin JM Martin-StPaul NK Jaeger C Rambal S 《Tree physiology》2012,32(4):464-477
Leaves of Mediterranean evergreens experience large variations in gas exchange rates over their life span due to aging and seasonally changing environmental conditions. Accounting for the changing respiratory physiology of leaves over time will help improve estimations of leaf and whole-plant carbon balances. Here we examined seasonal variations in light-saturated net CO(2) assimilation (A(max)), dark respiration (R(d)) and the proportional change in R(d) per 10 °C change in temperature (Q(10) of R(d)) in previous-year (PY) and current-year (CY) leaves of the broadleaved evergreen tree Quercus ilex L. A(max) and R(d) were lower in PY than in CY leaves. Differences in nitrogen between cohorts only partly explained such differences, and rates of A(max) and R(d) expressed per unit of leaf nitrogen were still significantly different between cohorts. The decline in A(max) in PY leaves did not result in the depletion of total non-structural carbohydrates, whose concentration was in fact higher in PY than CY leaves. Leaf-level carbon balance modeled from gas exchange data was positive at all ages. Q(10) of R(d) did not differ significantly between leaf cohorts; however, failure to account for distinct R(d) between cohorts misestimated canopy leaf respiration by 13% across dates when scaling up leaf measurements to the canopy. In conclusion, the decline in A(max) in old leaves that are close to or exceed their mean life span does not limit the availability of carbohydrates, which are probably needed to sustain new growth, as well as R(d) and nutrient resorption during senescence. Accounting for leaf age as a source of variation of R(d) improves the estimation of foliar respiratory carbon release at the stand scale. 相似文献
7.
Long-term hydraulic acclimation to resource availability was explored in 3-year-old Populus deltoides Bartr. ex Marsh. clones by examining transpiration, leaf-specific hydraulic conductance (G(L)), canopy stomatal conductance (G(S)) and leaf to sapwood area ratio (A(L):A(S)) in response to irrigation (13 and 551 mm year(-1) in addition to ambient precipitation) and fertilization (0 and 120 kg N ha(-1) year(-1)). Sap flow was measured continuously over one growing season with thermal dissipation probes. Fertilization had a greater effect on growth and hydraulic properties than irrigation, and fertilization effects were independent of irrigation treatment. Transpiration on a ground area basis (E) ranged between 0.3 and 1.8 mm day(-1), and increased 66% and 90% in response to irrigation and fertilization, respectively. Increases in G(L), G(S) at a reference vapor pressure deficit of 1 kPa, and transpiration per unit leaf area in response to increases in resource availability were associated with reductions in A(L):A(S) and consequently a minimal change in the water potential gradient from soil to leaf. Irrigation and fertilization increased leaf area index similarly, from an average 1.16 in control stands to 1.45, but sapwood area was increased from 4.0 to 6.3 m(2) ha(-1) by irrigation and from 3.7 to 6.7 m(2) ha(-1) by fertilization. The balance between leaf area and sapwood area was important in understanding long-term hydraulic acclimation to resource availability and mechanisms controlling maximum productivity in Populus deltoides. 相似文献
8.
We investigated how water and nutrient availability affect radiation-use efficiency (epsilon) and assessed leaf gas exchange as a possible mechanism for shifts in epsilon. We measured aboveground net primary production (ANPP) and annual photosynthetically active radiation (PAR) capture to calculate epsilon as well as leaf-level physiological variables (light-saturated net photosynthesis, Asat; stomatal conductance, gs; leaf internal CO2 concentration, Ci; foliar nitrogen concentration, foliar [N]; and midday leaf water potential, Psileaf) during the second (2001) and third (2002) growing seasons in sweetgum (Liquidambar styraciflua L.) and sycamore (Platanus occidentalis L.) stands receiving a factorial combination of irrigation and fertilization at the Savannah River Site, South Carolina. Irrigation and fertilization increased PAR capture (maximum increase 60%) in 2001 and 2002 for both species and annual PAR capture was well correlated with ANPP (mean r2 = 0.77). A decreasing trend in epsilon was observed in non-irrigated stands for sweetgum in 2001 and for sycamore in both years, although this was only significant for sycamore in 2002. Irrigated stands maintained higher gas exchange rates than non-irrigated stands for sweetgum in 2001 and for sycamore in both years, although foliar [N] and Psileaf were generally unaffected. Because Ci decreased in proportion to gs in non-irrigated stands, it appeared that greater stomatal limitation of photosynthesis was associated with decreased Asat. On several measurement dates for sweetgum in 2001 and for sycamore in both years, epsilon was positively correlated with gas exchange variables (Asat, gs, Ci) (r ranged from 0.600 to 0.857). These results indicate that PAR capture is well correlated with ANPP and that gas exchange rates modified by irrigation can influence the conversion of captured light energy to biomass. 相似文献
9.
10.
We investigated seed dormancy and germination in Ficus lundellii Standl. (Moraceae), a native species of Mexico's Los Tuxtlas tropical rain forest. In an 8-h photoperiod at an alternating diurnal (16/8 h) temperature of 20/30 degrees C, germination was essentially complete (96%) within 28 days, whereas in darkness, all seeds remained dormant. Neither potassium nitrate (0.05-0.2%) applied continuously nor gibberellic acid applied either continuously (10-200 ppm) or as a 24 hour pretreatment (2000 ppm) induced germination in the dark. Germination in the light was not reduced by a 24-h hydrochloric acid (0.1-1%) pretreatment, but it was reduced both by a 24-h pretreatment with either H(2)O(2) (0.1-5 M) or 5% HCl, or by more than 5 days of storage at 40 degrees C (4.5% seed water content). In a study with a 2-dimensional temperature gradient plate, seeds germinated fully and rapidly in the light at a constant temperature of 30 degrees C, and fully but less rapidly in the light at alternating temperatures with low amplitudes (< 12 degrees C) about the optimal constant temperature. The base, optimal and ceiling temperatures for rate of germination were estimated as 13.8, 30.1 and 41.1 degrees C, respectively. In all temperature regimes, light was essential for the germination of F. lundellii seeds. 相似文献
11.
We studied the effects of excess nitrogen added as nitrate (NO(3) (-)) or ammonium (NH(4) (+)), or both, on mineral nutrition and growth of beech (Fagus sylvatica L.) plants grown at pH 4.2 in Al-free nutrient solution or in solutions containing 0.1 or 1.0 mM AlCl(3). A high external concentration of NH(4) (+) increased the concentration of nitrogen in roots, stems and leaves. The root/shoot dry weight ratio was less in plants grown in the presence of NH(4) (+) than in plants grown in the presence of NO(3) (-). The concentration of phosphorus in the roots was increased and the concentration of potassium in all parts of the plant was decreased by NH(4) (+). A high external concentration of NO(3) (-) caused a decrease in phosphorus concentrations of the root, stem and leaf. Uptake of (45)Ca(2+) by roots was reduced in the presence of high concentrations of NH(4) (+) or NO(3) (-), and a combination of high concentrations of nitrogen and aluminum further reduced the uptake of (45)Ca(2+). Uptake of phosphate ((32)P) and concentrations of phosphorus in root and shoot were increased when plants were grown in the presence of 0.1 mM Al. Exposure to 1.0 mM Al, however, reduced the concentration of phosphorus in roots and shoots and the reduction was greater when plants were grown in the presence of a high external NO(3) (-) concentration. Aluminum binds to roots, and plants grown in the presence of 1.0 mM Al had a slightly higher concentration of aluminum in roots than plants grown in the presence of 0.1 mM Al, whereas the concentration of Al in the shoot was increased 2 to 3 times in plants exposed to 1.0 mm Al. Furthermore, the effects of 1.0 mM Al on uptake of other macronutrients were quite different from the effects of 0.1 mM Al. We conclude that 0.1 mM Al facilitates uptake and transport of phosphorus in beech and that between 0.1 and 1.0 mM Al there is a dramatic change in the effects of Al on uptake and transport of divalent cations and phosphorus. 相似文献
12.
Diurnal and seasonal variations in leaf hydraulic conductance in evergreen and deciduous trees 总被引：1，自引：0，他引：1
We studied changes in the hydraulic conductance of leaves (K(leaf)) between dawn and dusk during the growth period (July) and at midday at the beginning of autumn in four tree species. The main objectives of the study were to check the extent of diurnal and seasonal changes in K(leaf) and the relationships between K(leaf), irradiance and leaf gas exchange. Two evergreen (Aleurites moluccana and Persea americana) and two deciduous trees (Platanus orientalis and Quercus rubra) were studied. Leaf hydraulic conductance was measured every 2 h between 0700 and 1900 h in July and compared with values measured between 0900 and 1300 h in October. Other variables measured were photosynthetically active radiation (PAR), leaf conductance to water vapor (gL) and water potential (psiL). In July, K(leaf) varied by up to 75% in Pe. americana on a diurnal basis and by at least 44% in Q. rubra. The diurnal time course of K(leaf) showed a distinct increase between dawn and late morning (1100 h) and a subsequent decrease in the evening in A. moluccana and Pl. orientalis, whereas in the other two species, K(leaf) was highest just after dawn and lowest in the evening. In October, K(leaf) of all the species studied was lower than in July, with differences of 20 to 28% for A. moluccana and Pl. orientalis and of 66 to over 70% in Pe. americana and Q. rubra, respectively. Significant correlations were found between PAR and K(leaf) (in all species) as well as between gL and K(leaf) (in three out of four species). Leaf habit (evergreen or deciduous) did not influence absolute values of K(leaf) or its diurnal variation. 相似文献
13.
A new method is presented for measuring whole-shoot hydraulic conductance, K(T) (kg s(-1) MPa(-1)). The method was also used to determine other conductance values in maple (Acer saccharum Marsh.) stem segments of differing diameter including: K(h) (absolute conductance or conductance per unit pressure gradient, kg s(-1) m MPa(-1)), K(s) (specific conductance or K(h) per unit wood area, kg s(-1) m(-1) MPa(-1)), and LSC (leaf specific conductance or K(h) per unit leaf area, kg s(-1) m(-1) MPa(-1)). A regression of K(T) versus stem basal diameter, D (m), gave K(T) = 5.998 x 10(-2) D(1.402) (R(2) = 0.986 for D from 0.001 to 0.1 m) and a regression for leaf area, A(L) (m(2)), gave A(L) = 4.667 x 10(3) D(2.007) (R(2) = 0.981 for D from 0.001 to 0.3 m). More than 50% of the resistance to water flow in large shoots (0.1 m in diameter and 8 to 10 m long) was contained in branches less than 0.012 m in diameter, i.e., in the distal 1.5 m of branches. We used the regressions to predict the steady state difference in pressure potential, P, between the base of a shoot of diameter D and the average pressure potential at the apices of the shoot; the relation is given by P = 7.781 x 10(4) E D(0.605), where E is the average evaporative flux density (kg s(-1) m(-2)) in the leaves attached to the shoot. After comparing the predictions of this equation to field observations of E and leaf water potential and stomatal conductance, we concluded that the hydraulic conductance of large maple shoots is sufficiently low to prevent maximum stomatal conductance in maple leaves. 相似文献
14.
Effects of four N sources and two defoliation treatments on growth and nitrogenase activity of Gliricidia sepium (Jacq.) Walp seedlings were studied in a greenhouse. All nutrients were supplied in irrigation water to the sterile growing medium. The N sources were: (1) 100 mg l(-1) of N supplied as NO(3) (-) (high-NO(3) (-)), (2) 50 mg l(-1) of N supplied as NO(3) (-) and inoculation with Rhizobium spp. medium-NO(3) (-)), (3)100 mg l(-1) of N supplied as NH(4)NO(3), and (4) inoculation with Rhizobium spp without mineral N (N(2)). At 35 weeks after sowing, mean total biomass was 130.5, 50.5, 22.9 and 17.4 g seedling(-1) in the NH(4)NO(3), N(2), medium-NO(3) (-) and high-NO(3) (-) treatments, respectively. The root/shoot ratio was high in all of the N treatments (1.73-2.77) because the seedlings had big taproots. The medium-NO(3) (-) treatment completely inhibited nodulation, whereas seedlings in the N(2) treatment were profusely nodulated. At 32 weeks after sowing, groups of seedlings in the N(2) and high-NO(3) (-) treatments were subjected to 50 or 100% defoliation. Closed-chamber acetylene reduction assays of intact root systems were conducted to compare nitrogenase activity at 7, 14 and 28 days after defoliation (DAD). At 7 and 14 DAD, nitrogenase activity of completely and partially defoliated seedlings was about 10 and 60%, respectively, of that of undefoliated controls. At 28 DAD, nitrogenase activity of completely defoliated seedlings was twice the predefoliation value, whereas nitrogenase activity of partially defoliated seedlings was only 87% of the predefoliation value. Recovery of nitrogenase activity was strongly correlated with foliage regrowth in the completely defoliated seedlings, but not in the partially defoliated seedlings. Abundant belowground C and N reserves in the large taproot probably contributed to the rapid recovery from defoliation. Accumulation of belowground biomass may also improve defoliation tolerance of mature trees. 相似文献
15.
Temporal changes in inorganic and organic sulfur compounds (sulfate, glutathione, cysteine, methionine) were analyzed in xylem sap of 40-year-old Norway spruce (Picea abies (L.) Karst.) trees growing on acidic soils at a healthy and a declining stand in the Fichtelgebirge (North Bavaria, Germany). Studies were carried out (1) to quantify glutathione (GSH) transport in the xylem of spruce, (2) to study the significance of reduced sulfur versus sulfate (SO(4) (2-)) transport in the xylem, and (3) to compare total sulfur (S) transport in the xylem with the amount of foliar uptake of SO(2) in an air-polluted environment. Glutathione was the main reduced S compound in the xylem ranging in concentration from 0.5 to 5 &mgr;mol l(-1). Concentrations of inorganic SO(4) (2-) in the xylem sap were up to 50 times higher than those of GSH ranging from 60 to 230 &mgr;mol l(-1). During the growing season, concentrations of all S compounds in the xylem were highest in May (up to 246 &mgr;mol l(-1)) and decreased during summer and fall (up to 21 &mgr;mol l(-1)). On average, SO(4) (2-) concentrations in xylem sap were 30% higher at the declining site compared with the healthy site. Diurnal changes in organic S compounds were significant for GSH and cysteine with high concentrations during the night and low concentrations during the day. Diurnal changes in inorganic concentrations were not significant. Xylem sap concentrations of SO(4) (2-) and cysteine were twice as high and GSH concentrations were tenfold higher in surface roots than in branches. At both sites, transport of organic S was low (up to 3% of total S) compared to transport of SO(4) (2-). Annual transport of total S in the xylem (SO(4) (2-) was the main component) ranged from 60 to 197 mmol tree(-1) year(-1) at the healthy site and from 123 to 239 mmol tree(-1) year(-1) at the declining site. Although gaseous uptake of SO(2) was estimated to be similar at both sites (38 mmol tree(-1) year(-1); Horn et al. 1989), the ratio between annual gaseous uptake of SO(2) and transport of S in the xylem was 1:4 and 1:5 at the healthy and declining sites, respectively. 相似文献
16.
Leaves, the distal section of the soil-plant-atmosphere continuum, exhibit the lowest water potentials in a plant. In contrast to angiosperm leaves, knowledge of the hydraulic architecture of conifer needles is scant. We investigated the hydraulic efficiency and safety of Pinus pinaster needles, comparing different techniques. The xylem hydraulic conductivity (k(s)) and embolism vulnerability (P(50)) of both needle and stem were measured using the cavitron technique. The conductance and vulnerability of whole needles were measured via rehydration kinetics, and Cryo-SEM and 3D X-ray microtomographic observations were used as reference tools to validate physical measurements. The needle xylem of P. pinaster had lower hydraulic efficiency (k(s)?=?2.0?×?10(-4) m(2) MPa(-1) s(-1)) and safety (P(50)?=?-?1.5 MPa) than stem xylem (k(s)?=?7.7?×?10(-4) m(2) MPa(-1) s(-1); P(50)?=?-?3.6 to?-?3.2 MPa). P(50) of whole needles (both extra-vascular and vascular pathways) was?-?0.5 MPa, suggesting that non-vascular tissues were more vulnerable than the xylem. During dehydration to?-?3.5 MPa, collapse and embolism in xylem tracheids, and gap formation in surrounding tissues were observed. However, a discrepancy in hydraulic and acoustic results appeared compared with visualizations, arguing for greater caution with these techniques when applied to needles. Our results indicate that the most distal parts of the water transport pathway are limiting for hydraulics of P. pinaster. Needle tissues exhibit a low hydraulic efficiency and low hydraulic safety, but may also act to buffer short-term water deficits, thus preventing xylem embolism. 相似文献
17.
Leaf phenology, growth irradiance (i.e., photosynthetic photon flux (PPF) at the leaf surface) and photosynthetic capacity (A(area); measured at a PPF of 1000 micro mol m(-2) s(-1) and expressed on a leaf area basis) were investigated in early leaves (ELs) and late leaves (LLs) of Betula grossa Siebold & Zucc. trees. Early leaves first appeared on morphologically distinct long shoots and short shoots. The appearance of ELs, which was restricted to the bud break period, was followed by the successive appearance of LLs on long shoots only. Late leaves appeared successively until the middle of the growing season. Late leaves started to abscise around the middle of the growing season, whereas ELs on both long and short shoots did not abscise until near the end of the growing season. Solar irradiance was higher at the surface of LLs of late appearance than at the surface of either LLs of early appearance or ELs. Solar irradiance at the surface of ELs decreased after LLs appeared. In both long and short shoots, A(area) of ELs increased and then remained stable for 65-80 days before starting to decrease. Although A(area) was higher in LLs than in ELs for a short time in August, it started to decrease earlier in LLs than in ELs. Area-based nitrogen concentration (N(area)) was higher in LLs than in ELs after August. Although N(area) decreased slowly in ELs after August, it did not decrease in LLs. In both ELs and LLs, A(area)/N(area) decreased with time. The crown was thus characterized by a rapidly growing surface with young LLs having high A(area) and by shaded inner parts with ELs having stable low A(area). 相似文献
18.
Three pines species, three evergreen broadleaf trees, one C(3) and two C(4) perennial grasses of subtropical Taiwan were studied to elucidate the correlation between photosystem II (PSII) efficiency and photochemical reflectance index (PRI = (R(531) - R(570))/(R(531) + R(570))). Measurements were made at two sites differing in altitude (800 and 2600 m) over several growing seasons. At high elevation, potential PSII efficiency, measured by chlorophyll fluorescence (the ratio of variable to maximal fluorescence; F(v)/F(m)) at predawn, decreased with decreasing air temperature and varied greatly among species. At the lowest air temperature (-3 degrees C) studied, variation in F(v)/F(m) among species ranged from 0.33 to 0.72. In contrast, at low elevation where air temperature was moderate, seasonal variation in F(v)/F(m) was small in all of the study species. When species, elevation and season data were pooled, despite the high variation in F(v)/F(m) among species, a good correlation between F(v)/F(m) and PRI was observed. When compared at the same value of PRI, F(v)/F(m) of evergreen trees was higher than that of perennial grasses; however, when the minimum temperature on the measurement day was below 0 degrees C, F(v)/F(m) was underestimated relative to PRI. We conclude that PRI could be used as a remote indicator of photosynthetic function when air temperature is above 0 degrees C. 相似文献
19.
Increasing fruit load (from no berries present to 25, 50 and 100% of the initial fruit load) significantly decreased branch growth on 5-year-old coffee (Coffea arabica L.) trees of the dwarf cultivar 'Costa Rica 95', during their third production cycle. Ring-barking the branches further reduced their growth. Berry dry mass at harvest was significantly reduced by increasing fruit load. Dry matter allocation to berries was four times that allocated to branch growth during the cycle. Branch dieback and berry drop were significantly higher at greater fruit loads. This illustrates the importance of berry sink strength and indicates that there is competition for carbohydrates between berries and shoots and also among berries. Leaf net photosynthesis (P(n)) increased with increasing fruit load. Furthermore, leaves of non-isolated branches bearing full fruit load achieved three times higher P(n) than leaves of isolated (ring-barked) branches without berries, indicating strong relief of leaf P(n) inhibition by carbohydrate demand from berries and other parts of the coffee tree when excess photoassimilates could be exported. Leaf P(n) was significantly higher in the morning than later during the day. This reduction in leaf P(n) is generally attributed to stomatal closure in response to high irradiance, temperature and vapor pressure deficit in the middle of the day; however, it could also be a feedback effect of reserves accumulating during the morning when climatic conditions for leaf P(n) were optimal, because increased leaf mass ratio was observed in leaves of ring-barked branches with low or no fruit loads. Rates of CO(2) emission by berries decreased and calculated photosynthetic rates of berries increased with increasing photosynthetic photon flux (PPF) especially at low PPFs (0 to 100 micromol m(-2) s(-1)). The photosynthetic contribution of berries at the bean-filling stage was estimated to be about 30% of their daily respiration costs and 12% of their total carbon requirements at PPF values commonly experienced in the field (200 to 500 micromol m(-2) s(-1)). 相似文献
20.
《Journal of Sustainable Forestry》2013,32(1):39-52
Dried foliage (litter) of several herbaceous species was mixed with either vermiculite or two minesoils (topsoil and spoil) in containers planted with black locust (Robinia pseudoacacia), white ash (Fraxinus americana) or sweetgum (Liquidambar styraciflrua) seedlings in a greenhouse. Also, germinated seed of northern red oak (Quercus rubra) was planted in containers previously seeded with herbaceous species. In vermiculite, black locust growth was inhibited by 12 g litter additions of ranger alfalfa (Medicago sativa), birdsfoot trefoil (Lotus corniculatus), tall fescue (Festuca arundinacea), and Kentucky bluegrass (Poa pratensis), but stimulated by red clover (Trifolium pratense) litter. White ash growth was strongly inhibited by alfalfa and trefoil added to vermiculite at 12 and 18 g levels. In topsoil, sweetgum was strongly inhibited by alfalfa litter. Both sweetgum and red oak grew poorly in spoil, but seeded perennial ryegrass (Lolium perenne), orchardgrass (Dactylis glomerata) and fescue grew well. Some aspects of red oak growth were inhibited if grown in containers seeded with alfalfa, ryegrass, orchardgrass, red clover or fescue. Although isolation and identification of allelopathic compounds was not attempted, these results demonstrate that there may be important allelopathic interactions between herbaceous species and trees planted on minelands. 相似文献