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,80thd 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 thd,afterwards,the growth gradually resumed to normal on 80 thd,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(Pn) of B.chinensis was largely improved under low(L30) and medium(L60) addition of leaf litterrelative to CK.As time went by,there were no obvious differences between all treatments and CK on 80 thd.The variation trends of pigment contents on 50 thand 80thday 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 thand 80thday 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.