避雨环境下苹果幼树水分状态指标对干旱胁迫的响应

在避雨环境下进行土壤水势渐进式下降处理,研究了苹果树体水分状态指标对土壤干旱胁迫响应的敏感性,分析了不同水分状态指标与树体水分平衡之间的关系.结果表明: 树干直径日较差(MDS)及中午树干水势(Ψ_stem)对干旱胁迫最敏感.MDS对参考蒸散(ET₀)有明显的响应,且对干旱胁迫比较敏感,与ET₀呈显著正相关,相对树干直径日较差(MDS_r)与相对土壤水势(Ψ_{r soil})呈显著负相关,树干直径可实现连续性测量及自动化记录.Ψ_stem对土壤干旱胁迫较敏感,且与ET₀呈显著负相关,相对中午树干水势(Ψ_{r stem})与Ψ_{r soil}呈显著相关,目前叶水势和树干水势难以实现自动化连续性观测.其他树体水分状态指标,如黎明前叶水势(Ψ_pd)、树干直径日生长量(DG)和气孔导度(g_s)等对中度或重度干旱胁迫也有不同程度的响应,但总体上对土壤水势变化的响应不敏感.

Response of water status indicators in apple saplings to drought stress under shelter from rain.

The main tree water status indicators which sensitively responded to drought stress and related to tree water balance were investigated in treatment of progressive decrease of soil water potential under shelter from rain. The results showed that stem maximum daily shrinkage (MDS) and midday stem water potential (Ψ_stem) were most sensitive to drought stress among all the water status indicators. MDS not only significantly responded to reference crop evapotranspiration (ET₀), but also was sensitive to soil drought stress. MDS was significantly positively related to ET₀, and the correlation between relative stem daily maximum shrinkage (MDS_r) and relative soil water potential (Ψ_{r soil}) was highly significant. Moreover, the stems could be measured in succession and recorded automatically. Midday Ψ_stem was also sensitive to soil drought stress, and significantly negatively related to ET₀. The correlation between relative midday stem potential (Ψ_{r stem}) and Ψ_{r soil} was significant. But so far, it is difficult to automatically measure either leaf or stem water potential. Predawn leaf water potential (Ψ_pd), daily stem growth (DG) or stomatal conductance (g_s) also responded to drought stress to some extent under moderate or heavy drought stress, but they were not sensitive.