通过田间定位试验研究秸秆覆盖条件下施氮量对小麦氮素吸收利用及土壤硝态氮残留的影响。试 验包括覆盖（不覆盖和秸秆覆盖4500kg/hm2）和施氮量（0，75，150，225和300kg N/hm2）两个因素. 共10个处理. 重复3次。3年结果表明：秸秆覆盖对冬小麦吸氮t没有显著影响，但在偏旱年份，秸秆覆盖有利于提高氮肥利用效率。与不覆盖类似，秸秆覆盖冬小麦吸氪量在3年间呈持续增加趋势。不论秸秆覆盖还是不覆盖，施氟量小于等于150kg/hm2时。对土壤硝态氮残留量均没有显著影响；施氮量高于150kg/hm2时，土壤残留硝态氮量则显著 增加，0～200cm剖面出现明显的累积蜂，秸秆覆盖土壤残留硝态累积峰较不覆盖处理深40cm左右。

通过田间试验建立了冬小麦产量与灌水量及施氮量的关系模型，并作了模拟分析，以期研究旱地农田秸秆覆盖 条件下冬小麦增产的水氮条件。结果表明：秸秆覆盖的冬小麦能否增产与水肥供应关系密切。生育期间没有补充灌水时，覆盖增产主要取决于氮肥用量，氮肥投入较少时覆盖冬小麦经济产量能取得显著的增产效果；氮肥用量较高时产量低于 未覆盖处理。因此，在雨养农业区，通过配合适量的氮肥完全能够做到秸秆覆盖下增产增收。在不同氮肥用量前提下，覆盖的增产效果除了与生育期总灌水量有关外，还与灌水量在各生育期间的分配有关。因此，在有灌溉条件的地区，根据氮肥投入情况，将有限的水分配在作物最需要的时期才能取得秸秆覆盖下的节水高产。

在陕西渭北旱塬进行了4年田间小麦试验，研究了旱地不同栽培模式、施氮量和种植密度对土壤硝态氮残留累积的影响。结果表明。种植小麦4年后，0-200cm土壤剖面中残留硝态氮为29.87～462.59kg/hm2，且主要积累在80-160cm土层，土壤氮库不仅明显。且残留比前3年土壤剖面显著下移（前3年主要累积在100cm）。差异达显著和极显著水平；不同栽培模式和种植密度0-200cm土层硝态氮残留累积规律及其小麦籽粒吸氮量基本相似，排序均为：地膜覆盖>常规种植>秸秆覆盖>垄沟种植；随施氮量的增加土壤硝态氮残留量也相应增加，N0处理0-200cm土壤平均硝态氮残留量为57.69kg/hm2，N120处理平均为97.04kg/hm2，虽然高于无氮处理，但两者差异未达到显著水平，N240处理平均为355.43kg/hm2，比前者增加的幅度更大.其差异达到极显著水平。因施氮肥而增加的土壤硝态氮残留量为14.9～401.18kg/hm2。平均占4年施氮量的19.59%，其中地膜覆盖占26.07%，常规种植占20.98%。秸秆覆盖占7.46%，垄沟种植种植占13.87%。

Loss-of-function alleles of the sole heterotrimeric G-protein a subunit in Arabidopsis, GPA1, display defects in cell proliferation throughout plant development. Previous studies indicated that GPA1 is involved in brassinosteroid (BR) response. Here we provide genetic evidence that lossof-function mutations in GPA1, gpa1-2 and gpa1-4, enhance the developmental defects of bri1-5, a weak allele of a BR receptor mutant, and det2-1, a BR-deficient mutant in Arabidopsis. gpa1-2 bri1-5 and gpa1-4 det2-1 double mutants had shorter hypocotyls, shorter roots and fewer lateral roots, and displayed more severe dwarfism than bri1-5 and det2-1 single mutants, respectively. By using the Arabidopsis hypocotyl as a model system where the parameters of cell division and cell elongation can be simultaneously measured, we found that gpa1 can specifically enhance the cell division defects of bri1-5 and det2-1 mutants. Similarly, gpa1 specifically enhances cell division defects in the primary roots of bri1-5 and det2-1 mutants. Furthermore, an additive effect on cell division between gpa1 and bri1-5 or det2-1 mutations was observed in the hypocotyls, whereas a synergistic effect was observed in the roots. Taken together, these results provided the first genetic evidence that G-protein- and BR-mediated pathways may be converged to modulate cell proliferation in a cell/tissue-specific manner.

Heterotrimeric G protein signaling is important for cell-proliferative and glucose-sensing signal transduction pathways in the model plant organism Arabidopsis thaliana. AtRGS1 is a seven-transmembrane, RGS domain-containing protein that is a putative membrane receptor for D-glucose. Here we show, by using FRET, that D-glucose alters the interaction between the AtGPA1 and AtRGS1 in vivo. AtGPA1 is a unique heterotrimeric G protein subunit that is constitutively GTP-bound given its high spontaneous nucleotide exchange coupled with slow GTP hydrolysis. Analysis of a point mutation in AtRGS1 that abrogates GTPase-accelerating activity demonstrates that the regulation of AtGPA1 GTP hydrolysis mediates sugar signal transduction during Arabidopsis development, in contrast to animals where nucleotide exchange is the limiting step in the heterotrimeric G protein nucleotide cycle.