Leaf k interaction with water stress inhibition of nonstomatal-controlled photosynthesis

The relationship between leaf K⁺ concentration, in vitro dehydration, and nonstomatal-controlled photosynthesis was investigated using leaf slices that were vacuum infiltrated with media containing varying sorbitol concentrations. The leaf slices were from plants either supplied with complete or K⁺-deficient medium throughout a 35-day growth period. During this time, leaf K⁺ concentration, water potential, osmotic potential, and turgor pressure were monitored. Leaf K⁺ concentration averaged 239 micomoles per gram (fresh weight) in control plants, and dropped to 74.3 micromoles per gram (fresh weight) in K⁺-deficient plants. Less negative osmotic potentials and resultant turgor loss in K⁺-deficient plants indicated that the osmotically active pool of cellular K⁺ was lower in those plants.

The decrease in leaf K⁺ concentration enhanced the dehydration inhibition of photosynthesis. For example, increasing sorbitol from 0.33 to 0.5 molar during incubation inhibited photosynthesis in the controls by 14% or less. This same protocol resulted in an inhibition of photosynthesis by as much as 41% in K⁺-deficient tissue. In contrast to the data obtained with leaf slices, dehydration inhibition of isolated chloroplast photosynthesis was not affected by K⁺ status of parent plant material. These data are consistent with the hypothesis that one effect of leaf K⁺ deficiencies on photosynthetic response to dehydration may be mediated by extra-choloroplastic factors.

Ammonium ions, which facilitate stromal alkalinization, reversed the increased sensitivity of K⁺-deficient leaf slice photosynthesis to cell dehydration. However, NH₄⁺ had no effect on photosynthesis of K⁺-deficient leaf slices under nonhypertonic conditions. These data suggest that endogenous extra-chloroplastic K⁺ may modulate dehydration inhibition of photosynthesis, possibly by facilitating stromal alkalinization.

     

番茄叶片光合作用对快速水分胁迫的响应

采用聚乙二醇(PEG-6000)溶液控制番茄根际水势和叶片离体的方式设置了水分胁迫处理,测算了光合诱导过程中净光合速率、暗呼吸速率和CO2补偿点等光合参数的变化.结果表明:在1000μmol·m-2·s-1光诱导下,水分胁迫处理的番茄叶片净光合速率(Pn)达到最大值所需时间缩短为对照的1/3,气孔导度(gs)快速增大为对照的1.5倍.水分胁迫处理的番茄叶片光饱和点(LSP)比对照降低了65％～85％,而光补偿点(LCP)比对照增加了75％ ～100％,缩小了番茄叶片利用光能的有效范围.水分胁迫处理的番茄叶片最大光合能力(Amax)低于对照40％以上,暗呼吸速率(Rd)增大了约45％.可见,快速水分胁迫处理使番茄叶片气孔迅速开放,光合诱导初始阶段消失.水分胁迫导致植物利用光能的效率和潜力降低是植物生产力下降的重要原因,而气孔调节是番茄适应快速水分胁迫的重要生理机制.     

Chloroplast osmotic adjustment and water stress effects on photosynthesis

Previous studies have suggested that chloroplast stromal volume reduction may mediate the inhibition of photosynthesis under water stress. In this study, the effects of spinach (Spinacia oleracea, var `Winter Bloomsdale') plant water deficits on chloroplast photosynthetic capacity, solute concentrations in chloroplasts, and chloroplast volume were studied. In situ (gas exchange) and in vitro measurements indicated that chloroplast photosynthetic capacity was maintained during initial leaf water potential (Ψ_w) and relative water content (RWC) decline. During the latter part of the stress period, photosynthesis dropped precipitously. Chloroplast stromal volume apparently remained constant during the initial period of decline in RWC, but as leaf Ψ_w reached −1.2 megapascals, stromal volume began to decline. The apparent maintenance of stromal volume over the initial RWC decline during a stress cycle suggested that chloroplasts are capable of osmotic adjustment in response to leaf water deficits. This hypothesis was confirmed by measuring chloroplast solute levels, which increased during stress. The results of these experiments suggest that stromal volume reduction in situ may be associated with loss of photosynthetic capacity and that one mechanism of photosynthetic acclimation to low Ψ_w may involve stromal volume maintenance.     

Modulation of osmotic stress effects on photosynthesis and respiration by temperature in mesophyll protoplast of pea

Exposure of mesophyll protoplast of pea to osmotic stress decreases the rate of photosynthesis while stimulating marginally the respiratory rate of mesophyll protoplasts. The interaction of osmotic and temperature stress during the modulation of photosynthetic and respiratory rates of pea (Pisum sativum var Azad P1) mesophyll protoplasts was investigated. The protoplasts were exposed to either iso-osmotic (0.4 M) or hyper-osmotic (1.0 M) concentration of sorbitol at 15 degrees and 25 degrees C. The rates of photosynthesis and respiration were studied. At optimum temperature of 25 degrees C, there was a decrease in photosynthesis (< 10%) at hyper-osmoticum (osmotic effect), whereas respiration increased marginally (by about 15%). Low temperature (15 degrees C) aggravated the sensitivity of both respiration and photosynthesis to osmotic stress. At 15 degrees C, the decrease in photosynthesis due to osmotic stress was > 35%, while the respiratory rate was stimulated by 30%. The relative proportion of cytochrome pathway decreased by about 50% at both 15 degrees C and 25 degrees C while that of alternative pathway increased, more so, at 15 degrees C, when the mesophyll protoplasts were subjected to hyper-osmoticum stress. The titration experiments showed that extent of engagement of alternative pathway was higher, the slope value was slightly higher for 15 degrees C compared to 25 degrees C. Low temperature modulates the effect of hyper-osmoticum stress on photosynthesis and respiration, and results in increased participation of alternative pathway.     

基于FvCB模型分析盐分胁迫对棉花叶片光合作用的影响

为深入理解叶片光合特性对盐胁迫的响应机理,以棉花为试验材料,设置5个盐分(NaCl)浓度处理:0(CK)、50、100、150和200 mmol·L^-1,利用FvCB模型分析盐胁迫对棉花幼苗叶片光合特性的影响。结果表明:与CK相比,50和100 mmol·L^-1盐分处理增加了棉花叶片的最大羧化速率(V_{c max})和最大电子传递速率(J_max),但150和200 mmol·L^-1盐分处理显著降低了V_{c max}和J_max。叶片净光合速率(P_n)、叶肉导度(g_m)和暗呼吸速率(R_d)随盐分浓度升高而下降;与CK相比,50和100 mmol·L^-1盐分处理对g_m无显著影响,但P_n和R_d显著降低。150和200 mmol·L^-1盐分处理明显降低了P_n、g_m和R_d,且与0、50和100 mmol·L^-1盐分处理间存在显著差异;利用FvCB模型模拟了不同盐分胁迫下叶片净光合速率。与不考虑g_m的模拟结果相比,考虑g_m提高模拟值和实测值间的决定系数,并降低了平均绝对误差。棉花幼苗耐盐阈值为100～150 mmol·L^-1,随盐分浓度的增加,光合限制因素由叶肉因素转变为光合机构受损;引入g_m可以提高FvCB模型的模拟精度。     

The influence of water stress on leaf and stem photosynthesis in Spartium junceum L.

Stem and leaf photosynthetic responses to environmental parameters were studied in Spartium junceum L., a legume with chlorophyllous stems. Stem net photosynthesis (P_n) was consistently lower than leaf P_n. The low stem P_n was due to lower quantum yield, lower mesophyll conductance and lower CO₂-saturated P_n than that of leaf P_n. Stomatal limitations to leaf and stem P_n were similar (25%). Water stress caused a greater reduction in leaf P_n than that of stems. Leaf P_n was also reduced in water-stressed plants following rehydration. The reduced leaf P_n was associated with a reduced photon saturated P_n rate and a reduced CO₂ saturated P_n rate. Apparent quantum yield, mesophyll conductance and stomatal limitation of leaves were unaffected by water-stress. Stem P_n following rehydration was not influenced by the water-stress treatment. In general, leaf P_n was more responsive to environmental parameters and more sensitive to water stress than stem P_n. These data support the hypothesis that stem P_n has greater tolerance of water stress, but is limited to low P_n by biochemical means compared to leaves.     

Effect of water stress on leaf photosynthesis,chlorophyll content,and growth of oriental lily

The photosynthetic characterization of the oriental lily (Lilium) cv. Sorbonne and its response to increasing water stress were analyzed based on the net photosynthetic rate (P _n), stomatal conductance (g _s), intercellular CO₂ concentration (C_i), transpiration rate (E), water use efficiency (WUE), and stomatal limitation (Ls) in the Horqin Sandy Land of western China. A photosynthesis-PAR response curve was constructed to obtain light-compensation and light-saturation points (LCP and LSP), the maximum photosynthetic rates (P _max) and dark respiration rates (R _D). The growth of lilies in the pots was analyzed after anthesis. Various intensities of water stress (5, 10, and 20 days without water, and an unstressed control) were applied. The results indicated that drought stress not only significantly decreased P _n, E, g _s, photosynthetic pigment content (Chl a, Chl b, and Chl (a + b)) and increased intrinsic water use efficiency (WUE), but also altered the diurnal pattern of gas exchange. Drought stress also affected the photosynthesis (P _n)-PAR response curve. Drought stress increased LCP and R _D and decreased LSP and P _max. There were both stomatal and nonstomatal limitations to photosynthesis. Stomatal limitation dominated in the morning, whereas nonstomatal limitation dominated in the afternoon. Thus, drought stress decreased potential photosynthetic capacity and affected the diurnal pattern of gas exchange and P _n-PAR response curves, thereby reducing plant quality (lower plant height, flower length, flower diameter, and leaf area). Water stress is likely the main limitation to primary photosynthetic process in the lily. Appropriate watering is recommended to improve photosynthetic efficiency and alleviate photodamage, which will increase the commercial value of the lily in the Horqin Sandy Land.     

Acclimation of photosynthesis to low leaf water potentials

Photosynthesis is reduced at low leaf water potentials (Ψ_l) but repeated water deficits can decrease this reduction, resulting in photosynthetic acclimation. The contribution of the stomata and the chloroplasts to this acclimation is unknown. We evaluated stomatal and chloroplast contributions when soil-grown sunflower (Helianthus annuus L.) plants were subjected to water deficit pretreatments for 2 weeks. The relationship between photosynthesis and Ψ_l, determined from gas-exchange and isopiestic thermocouple psychometry, was shifted 3 to 4 bars towards lower Ψ_l, in pretreated plants. Leaf diffusive resistance was similarly affected. Chloroplast activity, demonstrated in situ with measurements of quantum yield and the capacity to fix CO₂ at all partial pressures of CO₂, and in vitro by photosystem II activity of isolated organelles, was inhibited at low Ψ_l but less in pretreated plants than in control plants. The magnitude of this inhibition indicated that decreases in chloroplast activity contributed more than closure of stomata both to losses in photosynthesis and to the acclimation of photosynthesis to low Ψ_l.     

Limitations due to water stress on leaf net photosynthesis of Quercus coccifera in the Portuguese evergreen scrub

Summary Gas exchange characteristics in leaves of the sclerophyll shrub Quercus coccifera were studied in the natural habitat in Portugal during spring and during the summer dry period. Compared to other sclerophyll species growing at the same site, photosynthesis in leaves of Quercus coccifera was less affected by water stress. Moderate water stress after six weeks of drought led to large decreases in stomatal conductance but no change in mesophyll photosynthetic capacity as compared to late spring. Leaf internal CO₂ pressure remained near 220 bar during diurnal courses in the spring. On midsummer days, leaf internal CO₂ decreased from a late morning value of 200 bar to a late afternoon value of approximately 150 bar. In contrast to Quercus suber (Tenhunen et al. 1984), restriction of CO₂ supply due to stomatal closure reduced net CO₂ uptake at midday and in the afternoon during midsummer. A decrease in leaf carboxylation efficiency and an increase in CO₂ compensation point at midday also played an important role in determining the diurnal course of net photosynthesis. During the late stages of drought in September, severe water stress led to reduction in mesophyll photosynthetic capacity and further reduction in leaf conductance. The observed decrease in mesophyll photosynthetic capacity was correlated with decrease in the daily minimum leaf water potential to greater negative values than-30 bar. At this time, CO₂ saturated photosynthetic rates decreased as much as 50% over the course of a day when measured at constant saturating light, 32° C leaf temperature, and a water vapor mole fraction difference between leaf and air of 30 mbar bar^-1.     

Salinity effects on leaf anatomy: consequences for photosynthesis

Increasing salinity led to substantially higher ratios of mesophyll surface area to leaf area (A^mes/A) for Phaseolus vulgaris and Gossypium hirsutum and a smaller increase for Atriplex patula, a salt-tolerant species. The increase in internal surface for CO₂ absorption did not lead to higher CO₂ uptake rates, since the CO₂ resistance expressed on the basis of mesophyll cell wall area (r_cell) increased even more with salinity. The differences among species in the sensitivity of photosynthesis to salinity in part reflect the different A^mes/A and r_cell responses.     

Drought stress effects on three cultivars of Eragrostis curvula: photosynthesis and water relations

Water stress effects were studied on three cultivars ofEragrostis curvula. Leaf water potential, RWC, total plantleaf area, green dry weight mass percentage and CO₂ gas-exchangeweremeasured during the onset of stress and after recovery. After 3 days of waterstress, RWC of cv Tanganyika plants was around 30–40% of controls,while RWC of cvs Ermelo and Consol was around 50–60% of controls.However midday and predawn water potentials were lower in cvs Tanganyka andErmelo than in cv Consol. After re-watering, RWC and water potentials recoveredonly in Consol plants. A strong decrease of leaf area was recorded in cvsErmeloand Consol during water stress (about 91–94% less than the leafarea of controls). Photosynthesis decreased as a function of the degree ofwaterstress severity in all cultivars. Also, light saturated photosynthesis,CO₂ quantum yield and light at which saturated photosynthesisoccurred, were strongly reduced by water stress. Recovery of photosynthesis wasfound in cv Consol after five days re-watering. Cv Consol showed a betterconservation of water and higher resistance to water stress than the other twocvs.     

Interactive effects of water,light and heat stress on photosynthesis in Fremont cottonwood

Fremont cottonwood seedlings are vulnerable to water stress from rapid water‐table decline during river recession in spring. Water stress is usually cited as the reason for reduced establishment, but interactions of water stress with microclimate extremes are more likely the causes of mortality. We assessed photosynthetic responses of Fremont cottonwood seedlings to water, light and heat stresses, which commonly co‐occur in habitats where seedlings establish. Under moderate temperature and light conditions, water stress did not affect photosynthetic function. However, stomatal closure during water stress predisposed Fremont cottonwood leaves to light and heat stress, resulting in greatly reduced photosynthesis beginning at 31 °C versus at 41 °C for well‐watered plants. Ontogenetic shifts in leaf orientation from horizontal to vertical, which occur as seedlings mature, reduce heat and light stress, especially during water stress. When compared with naturally occurring microclimate extremes, seedling stress responses suggest that reduced assimilation and photoprotection are common for Fremont cottonwood seedlings on exposed point bars where they establish. These reductions in photosynthesis likely have negative impacts on growth and may predispose young (<90‐day‐old) seedlings to early mortality during rapid water‐table declines. Interactions with heat and light stress are more important in these effects than water stress alone.     

C4 photosynthesis and water stress

Background

In contrast to C₃ photosynthesis, the response of C₄ photosynthesis to water stress has been less-well studied in spite of the significant contribution of C₄ plants to the global carbon budget and food security. The key feature of C₄ photosynthesis is the operation of a CO₂-concentrating mechanism in the leaves, which serves to saturate photosynthesis and suppress photorespiration in normal air. This article reviews the current state of understanding about the response of C₄ photosynthesis to water stress, including the interaction with elevated CO₂ concentration. Major gaps in our knowledge in this area are identified and further required research is suggested.

Scope

Evidence indicates that C₄ photosynthesis is highly sensitive to water stress. With declining leaf water status, CO₂ assimilation rate and stomatal conductance decrease rapidly and photosynthesis goes through three successive phases. The initial, mainly stomatal phase, may or may not be detected as a decline in assimilation rates depending on environmental conditions. This is because the CO₂-concentrating mechanism is capable of saturating C₄ photosynthesis under relatively low intercellular CO₂ concentrations. In addition, photorespired CO₂ is likely to be refixed before escaping the bundle sheath. This is followed by a mixed stomatal and non-stomatal phase and, finally, a mainly non-stomatal phase. The main non-stomatal factors include reduced activity of photosynthetic enzymes; inhibition of nitrate assimilation, induction of early senescence, and changes to the leaf anatomy and ultrastructure. Results from the literature about CO₂ enrichment indicate that when C₄ plants experience drought in their natural environment, elevated CO₂ concentration alleviates the effect of water stress on plant productivity indirectly via improved soil moisture and plant water status as a result of decreased stomatal conductance and reduced leaf transpiration.

Conclusions

It is suggested that there is a limited capacity for photorespiration or the Mehler reaction to act as significant alternative electron sinks under water stress in C₄ photosynthesis. This may explain why C₄ photosynthesis is equally or even more sensitive to water stress than its C₃ counterpart in spite of the greater capacity and water use efficiency of the C₄ photosynthetic pathway.Key words: C₃ and C₄ photosynthesis, stomatal and non-stomatal limitation, high CO₂, water stress     

Some effects of leaf posture on photosynthesis and yield in wheat

Canopy enclosures were used to study the photosynthesis of two winter wheat genotypes with contrasting leaf posture (E, erect; L, lax). Over the grain filling period, the net carbon dioxide fixation during the daytime was nearly always greater in E than in L. In general, a greater proportion of the fixation took place in the lower leaves of E than L. Because of the slower senescence of its lower leaves, the leaf area index of E was slightly but consistently higher than that of L and this appeared to account, in part, for the difference between the genotypes in canopy photosynthesis. However, during June and early July, when the leaf area indices were above three, the more uniform distribution of light in the canopy of E than in that of L appeared to be a cause of its higher rate of photosynthesis. Over the grain filling period, more dry matter was lost from the stems of L than from those of E. It is suggested that the shortfall of assimilate for grain filling was met, at least in part, by translocation of materials from the stems and that their greater depletion in L made up for the lower contribution from current assimilation in this genotype.     

Effect of oxygen on photosynthesis by spinach leaf protoplasts

The photosynthetic CO₂ fixation by spinach leaf (Spinacia oleracea L. var. Kyoho) protoplasts was inhibited by substituting an atmosphere of N₂ with one of either air (21% O₂) or 100% O₂. The inhibitory effect of 100% O₂ was greater than that of air. The mode of inhibition by 100% O₂ and air was competitive with respect to CO₂; Ki(O₂) value was 0.32 mM at pH 7 and 0.28 mM at pH 8.5 The labeling patterns of compounds in protoplasts exposed to ¹⁴CO₂ in light after transferring them from N₂ to O₂ atmospheres were examined. There was no detectable ¹⁴CO₂ incorporation into glycolate under anaerobic and O₂ atmospheres; a more marked labeling of glycine occurred under an oxidative environment compared to that under the anaerobic condition, presumably because of a rapid transformation of glycolate to glycine in the protoplasts.     

Short-term effects of salt stress on antioxidant systems and leaf water relations of pea leaves

In pea ( Pisum sativum L.) plants the effect of short-term salt stress and recovery on growth, water relations and the activity of some antioxidant enzymes was studied. Leaf growth was interrupted by salt addition. However, during recovery, growth was restored, although there was a delay in returning to control levels. Salt stress brought about a decrease in osmotic potential and in stomatal conductance, but at 48 h and 24 h post-stress, respectively, both parameters recovered control values. In pea leaves, a linear increase in the Na⁺ concentration was observed in salt treated plants. In the recovered plants, a slight reduction in the Na⁺ concentration was observed, probably due to a dilution effect since the plant growth was restored and the total Na⁺ content was maintined in leaves after the stress period. A significant increase of SOD activity occurred after 48 h of stress and after 8 h of the recovery period (53% and 42%, respectively), and it reached control values at 24 h post-stress. APX activity did not change during the stress period, and after only 8 h post-stress it was increased by 48% with respect to control leaves. GR showed a 71% increase after 24 h of salt stress and also a significant increase was observed in the recovered plants. A strong increase of TBARS was observed after 8 h of stress (180% increase), but then a rapid decrease was observed during the stress period. Surprisingly, TBARS again increased at 8 h post-stress (78% increase), suggesting that plants could perceive the elimination of NaCl from the hydroponic cultures as another stress during the first hours of recovery. These results suggest that short-term NaCl stress produces reversible effects on growth, leaf water relations and on SOD and APX activities. This work also suggests that both during the first hours of imposition of stress and during the first hours of recovery an oxidative stress was produced.     

Water stress effects on photosynthesis in different mulberry cultivars

The effect of water stress on photosynthesis was determined in five mulberry cultivars (Morus alba L. cv. K-2, MR-2, BC2-59, S-13 and TR-10). Drought was imposed by withholding water and the plants were maintained at different water potentials ranging from 0.5 -MPa to 2.0 -MPa. Photosynthetic rates, activities of ribulose-1,5-bisphosphate carboxylase and sucrose phosphate synthase, photosystem II activity and chlorophyll content were used as key parameters to assess photosynthetic performance. There was a marked variation in the photosynthetic rates and ribulose-1,5-bisphosphate carboxylase activity among the five mulberry cultivars subjected to water stress. Photosystem II (PSII) and sucrose phosphate synthase activities were also severely reduced as measured by drought conditions. Of the five mulberry cultivars, S-13 and BC2-59 showed higher photosynthetic rates, ribulose-1,5-bisphosphate carboxylase activity, high sucrose phosphate synthase activity and photochemical efficiency of PSII compared to the other varieties.     

The effects of 2, 4-dichIorophenoxyacetk acid altered chloroplast development on photosynthesis

We studied the changes in function and physical properties of isolated radish ( Raphonus sativus L. cv. Sparkler) lamellar membranes 48 h after chloroplast development was altered by 2, 4-(dichlorophenoxy)acet, tc acid. The number of chlorophyll molecules attendant to each electron transport chain was approximately 25% less in the chloroplasts from 2, 4-(dichlorophenoxy)acetic acid-treated plants than in chloroplasts from untreated plants. The maximal turnover rate of Photosystem I] in the treated chloroplasts was slightly less than half the turnover rate in normal chloroplasts. The efficiency of coupling between electron flux and ATP formation was not significantly different in the two chloroplast types. This hight efficiency of photophosphorylation in addition to normal membrane conductance to hydrogen ions indicates that the herbicide has not brought about a general deterioration of the membrane. A dramatic increase in the proton binding capacity of the lamellar membrane was observed in the treated chloroplasts. This increase in hydrogen ion buffering groups was largely accounted for by extrinsic membrane proteins bound to the exterior surface of the lamellar membrane. Although the addition of 2, 4-(dichloro-phenoxy) acetic acid to chloroplasts isolated from untreated plants caused concurrent uncoupling of ATP formation and inhibition of electron transport, our data show that these direct effects of the compound have little to do with its herbicidal action.     

Effect of water deficits on transpiration, photosynthesis and leaf conductance in cassava

Transpiration, net photosynthesis and leaf conductance decreased when leaf water potential dropped below -0.30 MPa. Both transpiration and net photosynthesis rates were considerably reduced before the leaves were visibly wilted at -0.95 MPa. Consequently, visual symptoms are unlikely to provide a useful index for characterizing water deficits in cassava ( Manihot esculenta Crantz cv. Llanera). Decreases in net photosynthesis closely followed decreases in transpiration and this suggests that stomatal closure controls both processes.     

水肥耦合对汉源花椒幼苗叶片光合作用的影响

以汉源花椒幼苗为试验材料,通过盆栽试验研究了不同水肥耦合处理对汉源花椒叶片气孔导度(Gs)、胞间CO_2浓度(Ci)、净光合速率(Pn)、蒸腾速率(Tr)、水分利用效率(WUE)和叶面饱和水汽压亏缺(Vpdl)日变化的影响,并探讨了汉源花椒光合特性与土壤田间持水量(FWC)、施肥量(包括施全量NPK、1/2NPK和不施肥,其中全量NPK含尿素150 kg N/hm~2、过磷酸钙60kg P_2O_5/hm~2和硫酸钾150 kg K_2O/hm~2)和环境因子间的关系。结果表明:各处理汉源花椒叶片Gs、Pn、Tr和Vpdl日变化均呈"单峰"型曲线,其峰值分别出现在10:00—12:00、10:00—12:00、14:00和14:00左右,没有出现光合"午休"现象;Ci最低值出现在10:00—12:00左右;WUE日变化呈"双峰"型曲线,峰值分别出现在10:00和16:00左右,但第2个峰值明显低于第1个峰值。NPK+50%FWC和1/2NPK+50%FWC两处理叶片Pn日变化峰值出现在12:00左右,而其他处理均出现在10:00左右。叶片Gs、Pn、Tr和WUE平均值均随施肥量的增加而增加,而Ci和V_(pdl)平均值随施肥量的增加而降低。叶片Gs、Pn和Tr平均值随土壤水分含量的增加总体上呈先增加后降低的趋势变化;Ci平均值总体上随土壤水分含量的增加而增加;WUE平均值随土壤水分含量的增加而降低;V_(pdl)平均值随土壤水分含量的增加呈先降低后增加的趋势变化。叶片Pn与地径(D)、苗高(H)、D~2H、叶绿素含量和chla/chlb比值呈显著正相关。为了促进植株生长和获得较高的叶片Pn和WUE,土壤水分应控制在35.9%—46.7%FWC。叶片Gs、Pn和Tr与光合有效辐射强度(PAR)呈显著正相关,Tr与气温的相关系数高于它与其他环境因子的相关系数,提高叶片Pn的最佳PAR为1263.6μmol m~(-2)s~(-1)。说明适宜的土壤水分含量和肥料施用量能延长汉源花椒叶片Pn达到峰值的时间,对提高叶片Pn和WUE及促进植株生长具有重要作用;PAR是影响叶片Gs和Pn的主要环境因子,气温是影响叶片Tr的首要环境因子。