Effects of Root Pruning on Non-Hydraulic Root-Sourced Signal, Drought Tolerance and Water Use Efficiency of Winter Wheat

Two pot experiments were conducted to study the effects of root pruning at the stem elongation stage on non-hydraulic root-sourced signals （nHRS）, drought tolerance and water use efficiency of winter wheat （Triticum aestivum）. The root pruning significantly reduced the root weight of wheat, but had no effect on root/shoot ratio at the two tested stages. At booting stage, specific root respiration of root pruned plants was significantly higher than those with intact roots （1.06 and 0.94 mmol g-1 s-1, respectively）. The soil water content （SWC） at which nHRS for root pruned plants appeared was higher and terminated lower than for intact root plants, the threshold range of nHRS was markedly greater for root pruned plants （61.1-44.6% field water capacity） than for intact root plants （57.9-46.1% field water capacity）. At flowering stage, while there was no significant difference in specific root respiration. The SWCs at which nHRS appeared and terminated were both higher for root pruned plants than for intact root plants. The values of chlorophyll fluorescence parameters, i.e., the effective photosystem II quantum yield （F PS II ）, the maximum photochemical efficiency of PS II （F v /F m ）, coefficient of photochemical quenching （qP）, and coefficient of non-photochemical quenching （NPQ）, in root pruned plants were significantly higher than in intact root plants, 7 d after withholding of water. Root pruned plants had significantly higher water use efficiency （WUE） than intact root plants in well-watered and medium drought soil, but not in severe drought condition. In addition, root pruning had no significant effect on grain yield in well-watered and medium drought soil, but significantly decreased grain yield in severe drought condition. In conclusion, the current study showed that root pruning significantly altered nHRS sensitivity and improved WUE of winter wheat in well-watered and medium drought soil, but lowered drought tolerance of winter wheat in severe drought soil. This suggests a possible direction of drought- resistance breeding and potential agricultural measure to improve WUE of winter wheat under semiarid conditions.

Effects of mechanical operation-induced root injury on maize growth and yield

A 2-year field experiment was conducted in 2015 and 2016 by using artificial root pruning to simulate mechanical root injury caused by agricultural machinery components and reveal its effects on maize growth and yield.Quasi-level orthogonal experimental design was employed to create orthogonal tables with four factors of interest,namely,pruning time(jointing stage,JS;big trumpet period,BTP),pruning method(unilateral pruning,UNP;bilateral pruning,BIP),pruning distance(5,10,and 15 cm)and pruning depth(5,10,and 15 cm).Results revealed that (1)maize growth was inhibited at the beginning of root pruning;(2)stem diameter(SD)and plant height(PHE)were smaller than those of the control check(CK)but exceeded the latter after 20 d of root pruning in JS;(3)SD and PHE were always smaller than those of the CK under root pruning in BTP;(4)T8(BTP,BIP,5 cm of pruning distance and 15 cm of pruning depth)can reach to a significant level(p<0.01).The vertical distribution and total dry weight(TDW)of maize roots in soil were affected by different root pruning treatments.When pruning in JS,the root ratio in 0-10 cm soil was 11.6%in T2(JS,UNP,a pruning distance of 10 cm and pruning depth of 10 cm).When pruning in BTP,the root ratio of 10-20 cm soil layer increased by 15%.However,the TDW of maize decreased,the largest of which occurred in T8 at 53%.With the exception of a 0.43%increase in T3(JS,UNP,15 cm of pruning distance and 15 cm of pruning depth),the maize yield of all other treatments decreased compared with that of CK,and the largest reduction was in T8 at up to 19.1%.This finding suggests that a small pruning distance and a large pruning depth greatly influence the growth and yield of maize before and during pruning in BTP.The influence of BIP is greater than that of UNP.These results provide evidence for the effects of mechanical root injury on maize growth and yield and serve as a reference for the selection of mechanical topdressing parameters.