立地条件和树龄对刺槐和小叶杨叶水力性状及抗旱性的影响

以形成黄土高原“小老树”的2种典型树种刺槐和小叶杨为对象,研究了立地条件(沟谷台地和沟间坡地)和树龄对两种树木叶水力学性质和抗旱性的影响,探讨“小老树”形成的水力生理机制.结果表明: 水分较好的沟谷台地上生长的两种树木的叶最大水力导度(K_max)明显大于水分较差的沟间坡地,叶水力脆弱性(P₅₀)也较高;随树龄增加,两种树木的K_max明显下降,但P₅₀差异不大.台地上生长的两种树木的叶表皮导度和PV曲线参数(膨压损失点时的相对含水量RWC_tlp、膨压损失点时的水势ψ_tlp、饱和含水量时的渗透势ψ_sat)均大于坡地;随树龄增加,两种树木的叶表皮导度显著下降,PV曲线参数出现不同程度的下降.两种树木K_max与ψ_tlp呈显著正相关,P₅₀与PV曲线参数之间存在一定的相关性,表明K_max与抗旱性之间存在一种权衡关系,P₅₀是反映两种树木的抗旱性特征之一.

Major terminologies and concepts in seed dispersal biology

In order to elucidate the hydro physiological mechanisms of the formation of ‘dwarf and aged’ trees, two typical  tree species Robinia pseudoacacia and Populus simonii on the Loess Plateau were chosen as the test objects to study their leaf hydraulic traits and drought resistance under effects of site conditions (gully bottom tableland and inter-gully slopeland) and tree age. For both R. pseudoacacia and P. simonii, the trees growing on the wet tableland had higher leaf maximum hydraulic conductance (Kmax) and hydraulic vulnerability (P50), and the Kmax decreased with tree age but the P50 had less difference, as compared with the trees growing on the dry slopeland. The trees growing on the tableland also had higher leaf epidermal conductance and PV curve parameters (including relative water content at turgor pressure loss point RWCtlp, water potential at turgor pressure loss point ψtlp, and osmotic potential at saturated water content ψsat), and the leaf epidermal conductance decreased significantly with tree age whereas the PV curve parameters had definite decrease. The Kmax was significantly positively correlated with ψtlp, and the P50 had definite correlations with PV curve parameters, suggesting that there existed a tradeoff relationship between Kmax and drought resistance, and P50was an important drought-resistant trait for the two tree species.