美洲黑杨凋落叶分解初期对小白菜生长的影响

采用盆栽试验,研究了美洲黑杨(Populus deltoides)凋落叶分解初期对受体植物小白菜(Brassica chinensis)生长和生理的影响。试验设置0、30、60和90 g/盆4个凋落叶施用水平(分别记作CK、L30、L60和L90)。同时,为检验凋落叶施入是否对土壤通气透水性产生明显影响进而影响受体植物的生长,用蒸煮后的凋落叶设置平行空白试验,即30、60、90 g/盆3个蒸著后的凋落叶处理(分别记作Z30、Z60和Z90)。将各处理的凋落叶分别与7 kg土壤混合,播种小白菜。在播种后50、80 d测定小白菜株高和生理指标。结果表明:1)高量(L90)凋落叶下小白菜的高生长和鲜重于50 d时被显著抑制,80 d时长势恢复正常;2)80 d时各处理净光合速率(Pn)与CK水平相当,色素含量略低于CK;3)50、80 d时,低(L30)、中(L60)量处理的超氧化物歧化酶(SOD)活性无明显变化,高量处理下SOD活性升高;4)各处理丙二醛(MDA)含量在50、80 d时与CK均无显著差异。总的来看,杨树各凋落叶量处理对小白菜的影响表现为:低、中量促进,高量抑制,而经蒸煮后的凋落叶处理间差异不显著。表明,低、中量杨树凋落叶在土壤中分解对小白菜生长及生理代谢的影响主要表现为促进作用,而施入高量凋落叶的初期,化感抑制作用明显。

Effects of decomposing leaf litter of Populus deltoides on the growth and physiology of Brassica chinensis

A pot experiment was conducted to study the effects of secondary metabolites released by decomposing Populus deltoides leaf litter on the growth and physiology of Brassica chinensis. In the main test four leaf litter application levels was set as 0, 30, 60 and 90 g/pot (respectively denoted as CK, L30, L60 and L90). Meanwhile, in order to test whether the physical form of the leaf litter could obviously influence the soil aeration, water permeability and even the growth of B.chinensis, the parallel blank test was performed with the steamed leaf litter, and the design of the test was set as same as the main test, namely 0, 30, 60 and 90 g/pot steamed leaf litter treatments (denoted as Z30, Z60 and Z90). Each pot contained 7 kg soil mixed with P.deltoides leaf litter and then sowed the seeds of B.chinensis. The height and physiological indices of B.chinensis were determined on 50^th, 80^th d after sowing. The results showed that: 1) The height and fresh weight of B.chinensis with high leaf litter addition (L90) of P.deltoides to the soil was significantly inhibited on 50^th d, afterwards, the growth gradually resumed to normal on 80^th d, while the height and fresh weight of B.chinensis in the other two treatments were markedly promoted consistently during the experimental period; 2) After 50 days of sowing, the net photosynthetic rate(R_n) of B.chinensis was largely improved under low(L30) and medium(L60) addition of leaf litter relative to CK. As time went by, there were no obvious differences between all treatments and CK on 80^th d. The variation trends of pigment contents on 50^th and 80^th day were substantially the same, both slightly lower than CK, yet, Chl a/b almost remained unchanged for all the time; 3) The activity of Superoxidedismutase(SOD) did not change apparently in low and medium addition of leaf litter, but increased in high addition from beginning to the end in this experiment; 4) The content of Malondialdehyde(MDA) on 50^th and 80^th day did not show any conspicuous differences whether there was leaf litter in soil or not, and no matter how much leaf litter was added to the soil within the amount range of litter designed in this experiment. In summary, the impacts that different amount of P.deltoides leaf litter militated on B.chinensis illustrated that: low and medium amount treatments of P.deltoides leaf litter mixed in soil stimulated the growth of B.chinensis, on the contrary high amount inhibited the growth. Besides, the result of parallel blank test showed that there was no evident disparity in regard to the growth and physiological indexes of B.chinensis among the steamed leaf litter treatments. On the whole, low and medium addition of P.deltoides leaf litter to the soil was absolutely conducive to the growth and physiological metabolism of B.chinensis, however, the suppression of allelopathic effect was remarkable with high addition of leaf litter in its initial decomposition stage.