亏缺灌溉和覆盖模式对芒果光合、光响应及干物质的影响

Effects of deficit irrigation and mulching modes on photosynthesis,light response and dry biomass of mango saplings

【目的】探讨亏缺灌溉和覆盖模式对芒果幼树光合特性、光响应曲线和干物质累积量的影响,寻找不同水分条件下适宜的光响应模型,为芒果科学水分管理提供实践参考。【方法】以2 a生芒果幼树为试验材料,设置3个灌水水平正常水分灌溉(W_(1))、轻度水分亏缺灌溉(W_(2))、重度水分亏缺灌溉(W_(3))和4种覆盖模式(裸地不覆盖(M_(0))、地表覆盖黑色地膜(M_(1))、地表覆盖松针(M_(2))、地表覆盖黑色遮阳网(M_(3)),共12个处理,测定不同处理的土壤体积含水率(VWC)和温度以及芒果幼树光合特性、光合-光响应曲线(净光合速率(P_(n)))-光强(PAR)曲线和主干、根、叶片干物质累积量,采用不同模型(直角双曲线模型(RH模型)、非直角双曲线模型(NRH模型)、指数模型(EX模型)和直角双曲线修正模型(MRH模型)对不同水分条件下的P_(n)-PAR曲线进行拟合,并对干物质累积总量与光合参数之间的关系进行分析。【结果】随着时间的延长,亏缺灌溉和覆盖模式对土壤VWC和温度有明显影响。当灌水量相同时,地表覆盖处理提高了土壤VWC和温度。相同PAR和覆盖模式下,P_(n)随着灌水量的增加而增大。相同PAR下,随着灌水量的减少,芒果幼树最大净光合速率(P_(n max))降幅增大。MRH模型适用于不同水分条件下P_(n)-PAR曲线的拟合(R^(2)>0.97),而RH模型、NRH模型和EX模型只适合高水分条件下(W_(1)和W_(2))芒果叶片P_(n)-PAR曲线的拟合(R^(2)>0.92)。当覆盖模式相同时,与W_(1)处理相比,W_(2)处理光合参数(P_(n)、蒸腾速率(T_(r))、瞬时水分利用效率(WUEi)、胞间CO_(2)浓度(C_(i))和主干、根、叶片干物质累积量总体无显著变化,W_(3)处理以上指标均明显降低。当灌水量相同时,与M_(0)处理相比,地表覆盖处理增加了P_(n)和主干、根、叶片干物质累积量。相关分析表明,干物质累积总量与P_(n)、T_(r)以及WUEi呈显著正相关。【结论】与正常水分灌溉处理相比,重度水分亏缺灌溉显著降低了芒果的光合作用和干物质累积量,轻度水分亏缺灌溉对芒果幼树生长没有产生不利影响,而地表覆盖处理有利于增强芒果幼树光合作用,促进干物质累积。4种模型中,MRH模型是拟合不同水分条件下芒果幼树P_(n)-PAR曲线的最适模型。

【Objective】This study explored photosynthetic characteristics,light-response,dry biomass accumulation and suitable light-response models of mango saplings under deficit irrigation combined with mulching modes to provide practical reference for scientific water management of mango.【Method】Two-year-old mango saplings were adopted as experimental materials with 12 treatments including 3 irrigation levels(normal water irrigation(W_(1)),mild water deficit irrigation(W_(2))and severe water deficit irrigation(W_(3))and 4 mulching modes(bare ground(M_(0)),black film mulching on ground(M_(1)),pine needles mulching on ground(M_(2))and shading net mulching on ground(M_(3)).Volumetric water content(VWC)and temperature of soil,photosynthetic characteristics,photosynthesis-light-response curve(net photosynthetic rate(P_(n))-light intensity(PAR)curve)and dry biomass accumulation of stem,root and leaf of mango saplings were measured,and the correlation between total dry biomass accumulation and photosynthetic parameters was analyzed.Various models including rectangular hyperbola model(RH model),non-rectangular hyperbola model(NRH model),exponential model(EX model)and modified rectangular hyperbola model(MRH model)were adopted to fit the Pn-PAR curves of mango saplings under different water conditions.【Result】Deficit irrigation and mulching modes had significant effects on VWC and soil temperature.With same irrigation amount,surface mulching increased VWC and soil temperature.Under same PAR and mulching mode,P_(n) increased with the increase of irrigation amount.Under same PAR,the drop of light-saturated net photosynthetic rate(P_(n max))increased with the reduction of irrigation amount.MRH model was suitable for fitting Pn-PAR curve under different water conditions(R^(2)>0.97),while RH model,NRH model and EX model were only suitable for fitting Pn-PAR curve of mango leaves under high water conditions(W_(1) and W_(2))(R^(2)>0.92).Under same mulching mode,photosynthetic parameters(P_(n),transpiration rate(T_(r)),intrinsic water-use efficiency(WUEi)and intercellular CO_(2) concentration(C_(i))and dry biomass accumulation in stem,root and leaf under W_(2) treatment did not change significantly compared with W_(1) treatment,while they were significantly decreased under W3 treatment.Compared with M_(0) treatment,mulching treatment increased Pn and dry biomass accumulation in stem,root and leaf at same irrigation amounts.Correlation analysis showed that total dry biomass accumulation was positively correlated with Pn,Tr and WUEi.【Conclusion】Compared with normal water irrigation treatment,severe water deficit irrigation significantly reduced photosynthesis and dry biomass accumulation of mango saplings,while mild water deficit irrigation had no adverse effect on growth of mango saplings.Mulching treatment was beneficial to increase photosynthetic characteristics and dry biomass accumulation of mango saplings.The MRH model was the most suitable to fit the Pn-PAR curve of mango saplings under different water conditions.