控制性分根区交替滴灌对苹果幼树形态特征与根系水分传导的影响

采用固定滴灌(根区一侧固定供水)、控制性分根区交替滴灌(根区两侧交替供水)和常规滴灌(紧贴幼树基部供水)3种灌水方式和3种灌水定额(固定滴灌和交替滴灌均为10、20和30 mm，常规滴灌为20、30和40 mm)，对比研究了控制性分根区交替滴灌对苹果幼树形态特征与根系水分传导的影响.结果表明： 交替滴灌的根区两侧土壤出现反复干湿交替过程，常规滴灌的根区两侧土壤含水率差异不显著.在灌水定额相同时，灌水侧的土壤含水率在3种灌水方式间差异不显著.与常规滴灌和固定滴灌相比，交替滴灌显著增加了苹果幼树的根冠比、壮苗指数和根系水分传导，在30 mm灌水定额处理下，交替滴灌的根冠比分别增加31.6%和47.1%，壮苗指数增加34.2%和53.6%，根系水分传导增加9.0%和11.0%.3种灌水方式下，根干质量和叶面积均与根系水分传导呈显著线性正相关.控制性分根区交替滴灌增强了苹果幼树根系水分传导的补偿效应，促进了根系对水分的吸收利用，有利于干物质向各个器官均衡分配，显著提高了根冠比和壮苗指数.

Effects of arsenic speciation on the phytochelatins (PCs) synthesis by Hydrilla verticillata

A hydroponic experiment was conducted to study the effects of different arsenic species \As(Ⅲ), As(V), and DMA\] at five concentrations (0, 0.3, 1.0, 3.0, and 5.0 mg·L-1) on the arsenic uptake and phytochelatins (PCs) synthesis by Hydrilla verticillata. The PCs contents were identified by reversed phase-high performance liquid chromatography (RP-HPLC). H. verticillata had an obvious arsenic uptake and accumulation. Low concentrations arsenic promoted the growth of H. verticillata, and the uptake of As(III) by H. verticillata was significantly higher than that of As(V) or DMA. As(Ⅲ) and As(V) promoted the synthesis of GSH, PC2, and PC4 significantly, and the synthesis was significantly positively correlated with the arsenic concentration in H. verticillata (P<0.05). DMA had little effects on the synthesis of PCs, with a detectable synthesis only at 0.3 mg·L-1 of DMA. With increasing concentration of As(Ⅲ), the synthesis of GSH and PC2 decreased after an initial increase, but the synthesis of PC4 increased. W ith the increasing concentration of As(V), the synthesis of GSH increased first and decreased then, while the synthesis of PC2 and PC4 presented an increasing trend. Very few PC3 was synthesized in all treatments except at 0.3 mg·L-1 of the test arsenic species. This study indicated that the synthesis of PCs was sensitive to the stress of As(Ⅲ) and As(V), and the PCs could be used as an biomarker indicating the stress of these two As species on H. verticillata.