森林土壤氮素可利用性的影响因素研究综述

Nitrogen cycling in forest ecosystems has been one of the focuses widely concerned by ecologists in the past decades. Well understanding the pattern of N cycling and N availability in different forest ecosystems all around the world will be of theoretically and practically great significance for studying and resolving the problems of global climate change and biodiversity loss.This paper reviewed the biological and non-biological factors affecting soil N availability in forest ecosystems,and briefly discussed the problems in studying N availability.

土壤活性氮动态变化及氮素可利用性对紫云英翻压量的响应

通过田间定位试验,研究了减量化肥紫云英不同翻压量下土壤活性氮的含量、动态变化及氮素可利用性,探讨了紫云英鲜草的适宜翻压量和土壤氮素利用效率,为双季稻合理施用氮肥提供理论依据。在稻-稻-紫云英轮作体系典型时期紫云英翻压前、早稻分蘖盛期、早稻成熟期、晚稻分蘖盛期、晚稻成熟期分别采集土壤样品,监测稻田土壤微生物量氮(MBN)、可溶性有机氮(DON)含量动态变化及氮素可利用性,并分析晚稻成熟期土壤铵态氮(NH+4-N)和硝态氮(NO-3-N)含量。结果表明:与对照(CK)处理相比,各施肥处理均提高了土壤全氮(TN)、NH+4-N和NO-3-N含量,增幅分别为10.4%~21.2%、10.3%~44.1%和14.7%~52.9%。在翻压紫云英15.0~22.5 t·hm^(-2)时,土壤TN、NH+4-N和NO-3-N含量均随紫云英还田量增多而提高,之后则随还田量的增多而降低。与常规施肥处理相比,化肥减施下紫云英各翻压量处理均提高了土壤MBN、DON及活性氮含量,增幅分别为7.0%~28.7%、8.5%~22.5%和5.8%~26.6%,且随紫云英翻压量的增加呈先增加后降低的变化趋势,MBN和活性氮含量均在翻压量22.5 t·hm^(-2)时最高,DON含量在翻压量30.0 t·hm^(-2)时最高。MBN/TN在翻压量22.5 t·hm^(-2)时最高,DON/TN在翻压量30.0 t·hm^(-2)时最高。各处理不同时期土壤MBN、DON含量及MBN/TN、DON/TN有明显波动,总体来看,土壤MBN含量及MBN/TN在早稻分蘖盛期明显降低,早稻成熟期有所回升,至晚稻成熟期又逐渐降低;土壤DON含量及DON/TN在早稻成熟期降至最低,至晚稻成熟期再次上升。研究表明,减施40%化肥条件下长期翻压紫云英不仅能增加土壤活性氮含量,同时有利于提高土壤氮素可利用性,紫云英翻压量22.5~30.0 t·hm^(-2)时效果最好。

Peashrub Community May Accelerate the Successional Process in a Meadowland-Peashrub-Birch Sere

Net N mineralization and nitrification were determined using the closed_top PVC tube in situ incubation method in a subalpine meadow (Saussurea iodostegia Hance + Carex capillaris L.)→shagspine peashrub (Caragana jubata (Pall.) Poir) shrubland→ribbed birch (Betula costata Trautv.) successional sere. The ability of the three communities to supply available N was comparatively studied. The results showed that there were apparent seasonal changes in the inorganic N pools (including NH + 4_N and NO - 3_N) and net N mineralization and nitrification rates in the three sites. There were generally no significant differences in the inorganic N pools among sampling events. But the NH + 4_N concentration in both birch (P<0.01) and meadow (P<0.01) sites was significantly higher than that in peashrub site in June 1996, and the NO - 3_N concentration in peashrub site was significantly higher than that of meadow site (P<0.05) in August 1996. The annual net N mineralization and nitrification rates in peashrub site (16.01 kg·hm -2 ) were higher than in birch (12.05 kg·hm -2 ) and meadow sites (1.64 kg·hm -2 ). The annual net nitrification rate in peashrub site (11.37 kg·hm -2 ) was higher than in meadow site (10.90 kg·hm -2 ) and much lower than in birch site (14.36 kg·hm -2 ). We conclude that the ability of peashrub shrubland soil to supply available N for plant uptake and the ability to prevent available N from denitrification and leaching were higher than that of the other two sites. The leguminous peashrub might play a potential role in supplying more N, which in turn facilitate the invasion of birch saplings during the successional processes.

易分解有机碳对不同恢复年限森林土壤激发效应的影响

土壤有机碳库作为陆地生态系统最大的碳库,其微小的改变都将引起大气CO2浓度的急剧改变。易分解有机碳的输入可以通过正/负激发效应加快/减缓土壤有机碳(SOC)的矿化,并最终影响土壤碳平衡。以长汀县不同恢复年限森林(裸地、5年、15年、30年马尾松林以及天然林)土壤为研究对象,通过室内培养向土壤中添加13C标记葡萄糖研究易分解有机碳输入对不同恢复阶段森林土壤激发效应的影响。研究结果表明,易分解有机碳输入引起的土壤激发效应的方向和强度因不同恢复阶段而异。易分解有机碳输入的初期对各恢复阶段森林土壤均产生正的激发效应,然而随着时间的推移,15年、30年马尾松林以及天然林相继出现负的激发效应。从整个培养期(59 d)来看,易分解有机碳的输入促进了裸地与5年生马尾松林土壤有机碳的矿化,有机碳的矿化量分别提高了131%±27%与25%±5%;但是减缓了15年生马尾松林土壤有机碳的矿化,使其矿化量减少了10%±1%;然而,易分解有机碳输入对30年生马尾松林及天然林土壤有机碳的矿化则无明显影响。土壤累积激发碳量与葡萄糖添加前后土壤氮素的改变百分比呈显著正相关关系(R^2=0.44,P<0.05),表明易分解有机碳输入诱导的土壤激发效应受土壤氮素可利用性的调控,土壤微生物需要通过分解原有土壤有机碳释放的氮素来满足自身的需求。

Expression Patterns of Nine Ammonium Transporters in Rice in Response to N Status

Nitrogen use efficiency （NUE） was very low in China and a loss of as much as 7070 of the applied nitrogen fertilizers was reported in high-yielding rice fields. In order to investigate the molecular basis of high-affinity ammonium transport or uptake into rice （Oryza sativa L.）, we analyzed the expression profiles of nine ammonium transporters （AMT）, three each of OsAMT1, OsAMT2 and OsAMT3, at two different N requirement stages （young seedling stage and tillering stage） of rice growth as well as the changes in these expression patterns according to external N status using real-time reverse transcription polymerase chain reaction （RT-PCR）. The results suggested that the nine OsAMT genes were expressed in different organs of rice plants, including mature roots, new roots, stems, old leaves and new leaves and that the expression patterns were organ specific and independent of the positions of the corresponding proteins in the phylogenetic tree. OsAMT1;1, 3;2 and 3;3 were expressed in the roots and shoots, primarily old leaves, OsAMT1;2 and 1;3 mainly in the roots, and OsAMT2;1, 2;2, 2;3 and 3;1 mainly in the shoots, primarily in new leaves, and relatively more in the stems than other genes. The expression patterns at the two different N requirement stages were the same; however, at the tillering stage with greater N requirements, the OsAMTs transcript levels were greater than those at the young seedling stage with low N requirements. N starvation for 48 h up-regulated OsAMT1;1, 1;2, 3;1, 3;2, 3;3 and down-regulated OsAMT1;3 mRNA abundance. Following N starvation, NH4＋ and NH4NO3 re-supply down-regulated OsAMT1;2 and 3;3 and up-regulated OsAMT1;3, whereas NO3 re-supply down-regulated OsAMT1;1 and 1;2. These suggested that the organ-specific expression pattern of OsAMT could be regulated by N requirement and external N status.

Effect of Nitrogen Starvation on the Responses of Two Rice Cultivars to Nitrate Uptake and Utilization

Ammonium(NH+4) is the main nitrogen(N) form for rice crops, while NH+4near the root surface can be oxidized to nitrate(NO-3)by NH+4-oxidizing bacteria. Nitrate can be accumulated within rice tissues and reused when N supply is insufficient. We compared the remobilization of NO-3stored in the tissue and vacuolar between two rice(Oryza sativa L.) cultivars, Yangdao 6(YD6, indica)with a high N use efficiency(NUE) and Wuyujing 3(WYJ3, japonica) with a low NUE and measured the uptake of NO-3, expression of nitrate reductase(NR), NO-3transporter genes(NRTs), and NR activity after 4 d of N starvation following 7-d cultivation in a solution containing 2.86 mmol L-1NO-3. The results showed that both tissue NO-3concentration and vacuolar NO-3activity were higher in YD6 than WYJ3 under N starvation. YD6 showed a 2- to 3-fold higher expression of OsNRT2.1 in roots on the 1st and 4th day of N starvation and had significantly higher values of NO-3uptake(maximum uptake velocity, Vmax) than the cultivar WYJ3.Furthermore, YD6 had significantly higher leaf and root maximum NR activity(NRAmax) and actual NR activity(NRAact) as well as stronger root expression of the two NR genes after the 1st day of N starvation. There were no significant differences in NRAmax and NRAact between the two rice cultivars on the 4th day of N starvation. The results suggested that YD6 had stronger NRA under N starvation, which might result in better NO-3re-utilization from the vacuole, and higher capacity for NO-3uptake and use, potentially explaining the higher NUE of YD6 compared with WYJ3.

Congeneric invasive versus native plants utilize similar inorganic nitrogen forms but have disparate use efficiencies

Aims Soil inorganic nitrogen(N)has long been recognized to play an important role in plant invasions.Whilst comparing the N use strategies of multiple invasive versus native plant congeners along an entire N gradient is key to understanding plant invasion success,there are few related studies.Methods We conducted a potted experiment with six invasive and native congeneric pairs,which were subjected to 11 nitrate/ammonium(NO3−/NH4+)ratios(i.e.100%NO3−at one end and 100%NH4+at the other end),each with low-and high-N levels.Each species–N combination was replicated eight times,and thus there were 2112 pots in total.We measured the following traits:the total biomass,growth advantage,biomass allocation,leaf chlorophyll content and low-N tolerance.Important Findings Invasive and native congeners grew well at any NO3−/NH4+ratios,and their responses of growth,allocation and tolerance were approximately parallel along the 11 NO3−/NH4+ratios across two N levels.Plant invaders grew larger and had greater chlorophyll contents,higher root biomass allocation and stronger low-N tolerance than their congeneric natives.These findings suggest that invasive and native plant congeners may utilize similar inorganic N forms(i.e.NO3−and NH4+)across an entire N composition gradient and that higher N use efficiencies could favor alien plants to invade new plant communities where congeneric natives are dominants.