The objectives of this study were to: (1) characterize the evolutional tendency of the non-hydraulic root-sourced signal (NRS) from wheat wild relatives to its modern hexaploid species, and (2) test whether species sensitivity to the NRS was allied with their drought tolerance profiles. The NRS was judged to begin when there was a significant lowering of stomatal conductance without change in leaf relative water content (RWC). The lethal soil water content (LSWC) was operationally characterized as the soil water content (SWC) at the drying lethal point of wheat plants. The threshold of soil water content (TSWC) at which the NRS was triggered, and the LSWC differed amongst six wheat species. For "MO1" and "MO4" representing 'diploid' species, the TSWC and the LSWC were initiated successively at about 51% FWC (field water capacity) and about 30% FWC, respectively. Conversely, "Plateau 602" and "Longchun 8139-2" (modern hexaploid species) exhibited the TSWC and the LSWC between about 68% FWC and less than 14% FWC, a much wider threshold range (TR). Increasing TSWC was significantly correlated with decreasing LSWC (r=0.9464**). The widened TR from the TSWC to the LSWC was also significantly correlated with longer survival days (SD) and higher maintenance ratio of grain yield (MRGY), respectively (r=0.9411** and 0.8068*, respectively). Meanwhile, those species having higher TSWC had the least reduction ratio of stomatal conductance under the decreasing soil moisture from −0.2 to −1MPa. This suggests that advances in yield performance and drought tolerance would be made evolutionally by targeted selection for an earlier onset of NRS.

Interrelationship among abscisic acid (ABA) content, accumulation of free polyamines and biosynthesis of β-N-oxalyl-L-α,β-diaminopropionic acid (ODAP) was studied in grass pea (Lathyrus sativus L.) seedlings under drought stress induced by 10% polyethylene glycol (PEG6000). Increase of ABA content occurred prior to that of ODAP and polyamine contents, and was found significantly positive correlation between ABA content and ODAP content. Addition of exogenous ABA increased ODAP content in leaves. On the other hand, pretreatment with α-difluoromethylarginine (DFMA), a polyamine biosynthesis inhibitor, significantly suppressed the accumulation of free putrescine (Put), free spermidine (Spd) and free spermine (Spm), which in turn inhibited biosynthesis of ODAP in well-watered leaves. Meanwhile, addition of exogenous Put alleviated DFMA-induced inhibition on the biosynthesis of Put and Spd, but did not affect the biosynthesis of Spm and ODAP in well-watered leaves. Same result was also achieved in drought-stressed leaves. Increasing accumulation of ODAP was significantly correlated with increasing Spm content (R=0.7957**) but not with that of Spd and Put. Therefore, it can be argued that ABA stimulated the biosynthesis of ODAP simultaneously with increasing the level of free Spm under drought stress condition.

The effects of exogenous abscissic acid (ABA) application on the antioxidant defenses were investigated in grass pea (Lathyrus sativus L.) seedlings. Four treatment combinations of ABA (1×10-3 nM ABA) and PEG (10% polyethylene glycol, PEG 6000) were designed to evaluate their short-term (48h) effect: (1) Well-watered group (Control group1), (2) PEG treatment, (3) ABA treatment, and (4) PEG+ABA treatment. In addition, 2 other treatments were used to evaluate the long-term (15d) effect of ABA: well-watered group (Control group2) and ABA treatment. Time-course analyses of ABA content, the production of malondialdehyde (MDA) and H2O2, and the activities of superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR) and peroxidase (POD) in water-stressed leaves showed that a significant increase in ABA content preceded that of MDA and H2O2 in long term experiment, which was followed by a substantial increase in the activities of four antioxidant enzymes. Under the short-term drought stress, ABA application promoted the activities of antioxidant enzymes, and reduced the accumulation of MDA and H2O2 significantly. On the contrary, long term application of exogenous ABA increase the generation of MDA and H2O2 significantly. It could be argued that during a successive application of exogenous ABA, ABA played a dual role by which the beneficial role in the initial stage shifted to a detrimental one under prolonged treatment in up-regulating protective defense strategies in plants.

The aim of this study was to investigate the spatial distribution patterns of soil seed bank of Stipagrostis pennata (Trin.) de Winter during different seasons in the Gurbantonggut Desert of north-west China.Results indicated that spatial patterns of the soil seed bank of S. pennata were similar to the distribution patterns of its associated standing vegetation, and there was a significant variation in soil seed densities among the different parts of the dunes.The highest soil seed density was found on the top of sampled dunes and in the soil of the underlayers of standing vegetation beds of S. pennata.The number of seeds stored in the soil decreased with distance from established stands of this grass species.Moreover, during secondary seed dispersal, which is air-borne in the windy season, a small proportion of seeds was also trapped by other plant species.Furthermore, the directional density distribution of seeds was strongly associated with the directions of the prevailing threshold wind (X6ms 1), and higher soil seed densities usually occurred on the leeward side of the vegetation stands.Based on these investigations, wind is, probably, the key factor in forming the spatial patterns of S. pennata seed banks in the region.On the other hand, grazing affected the quality and quantity of S. pennata seed storage, as a result of delayed development and the above-ground shoots being damaged by grazing.This occurred in spring to early summer, which is the most suitable growth season for the grass.Nevertheless, grazing had little influence on the spatial distribution patterns of the seed bank over all seasons.Germination trials showed that the percentage of viable soil seeds increased continuously throughout summer and autumn.The results also revealed the clear ecological characteristics influencing the population distribution of S. pennata.

A field experiment was conducted at the Haiyuan Experimental Station (36º34′N, 105º39′E), in a semiarid region of China, from 2000 to 2003 for rain-fed spring wheat (Triticum aestivum) production to maximize the utilization of low rainfall. This paper reports the two field cultivations of rainwater harvesting with a sowing in the furrow between film-covered ridges (SFFCR), and with a sowing in the holes on film-covered ridges (SHFCR). At the same time, the periods and indices of supplemental irrigation during the whole growth stage of rain-fed spring wheat were also studied. The periods of supplemental irrigation included the three-leaf stage (irrigated once), the elongation stage to flowering stage (irrigated twice), and the flowering stage to filling stage (irrigated once). The indices of supplemental irrigation during the whole growth stage of rain-fed spring wheat must reach over 59 and 40 mm in order to realize the 2250 and 2000kg ha 1 yield, respectively. This research also presented such a concept of efficient water saving supplemental irrigation, which was considered as a new index of water saving irrigation. The experimental result showed that the efficiency of water saving supplemental irrigation of field cultivation with SFFCR was 5.5-5.8%, and with SHFCR was 9.4-9.6%. The efficiency of water saving supplemental irrigation of field cultivation with SHFCR was improved by 40.4% in comparison with SFFCR. Consequently, in this region, the integration of rainwater harvesting and supplemental irrigation can play a crucial role in the improvement of rain-fed spring wheat yields and water use.