带膜还田时玉米秸秆的腐解率和还田层的温湿度变化趋势

采用尼龙网袋法对河西绿洲灌区带膜还田时玉米秸秆的腐解率及其还田层的温、湿度变化趋势进行分析,旨在为当地玉米秸秆还田提供理论依据和技术支撑。结果表明,秸秆还田在早晨8∶00左右可以提高土壤表层温度,在傍晚8∶00左右可以减缓土壤温度降低,其中翻压带膜还田时,秸秆还田层的日均相对湿度、最大相对湿度和最小相对湿度均高于覆盖带膜还田,但是相对湿度的日较差却低于覆盖带膜还田。同时,还田层的日最低温度高于覆盖带膜还田,而日均温度、最高温度和温度日较差却低于覆盖带膜还田。还田层温度、相对湿度和腐解时间是还田秸秆腐解的主要影响因子,其中还田层的温度影响最大,相对湿度和腐解时间其次。秸秆覆盖带膜还田时,还田层温度和相对湿度对还田秸秆的腐解起主要作用,腐解时间起次要作用。秸秆翻压带膜还田时,还田层温度、相对湿度和腐解时间三者对还田秸秆的腐解率均起主要作用。翻压带膜还田30天进入秸秆腐解高峰期,月腐解率达15%~16%,覆盖带膜还田60天进入腐解高峰期,月腐解率达11%~16%。经过180天的腐解后,翻压带膜还田的秸秆累积腐解率为72.5%,覆盖带膜还田秸秆的累积腐解率为56.0%。可见,在河西绿洲灌区进行秸秆带膜还田时,翻压带膜还田要好于覆盖带膜还田。     

宁夏南部退耕坡地与宜林荒山植被恢复方式对比研究

以宁夏南部黄土丘陵区、土石山区退耕坡地、宜林荒山为试验区,以植被恢复效果为依据,研究了几种技术措施在宁夏南部地区的适用性。结果证明,与任垦任牧相比,自然封禁或人工造林3年后,植物种类分别增加13个、4.75个,增加百分比达到76%~126.8%;植被盖度增加49.8%~14.9%;基质(下垫面)有机质、全量养分、速效养分、0~20cm土层粉粒百分比分别较对照提高8.2g/kg、0.79g/kg、5.8mg/kg、6.54%;减流56.9%~91.5%,减沙61.3%~94.7%;自然封禁区草被盖度、高度、单位面积鲜草产量、干草产量分别增加14.9%、16.5%、38.1%、38.3%;人工造林区辽东栎树高、胸径、单株材积年平均增长量分别为88.3%、87.9%、89%。可见,自然封禁和人工造林都是宁南植被恢复的好方法,两种措施相对比,人工造林区>自然封禁区,退耕坡地>宜林荒山地;建议在有条件的地区尽量多采用人工造林方法,并尽可能选用辽东栎作为乔层树种。     

促腐条件下小麦玉米秸秆还田土壤养分变化特征研究

采用盆钵培养法,模拟定西市李家堡镇典型的黄土高原旱作农业区旱作覆膜方式,通过秸秆添加腐解剂还田研究小麦秸秆、玉米秸秆腐解120 d土壤养分含量的动态变化特征。结果表明:在小麦秸秆、玉米秸秆120 d的腐解过程中,各处理土壤有机质、碱解氮、全氮的增加速率一致表现为先增后减,土壤磷素、钾素的增加速率变化趋势为增—减—增—减;添加腐解剂处理的土壤养分增加速率均大于秸秆直接还田(对照),培肥土壤效果明显;小麦、玉米秸秆添加腐解剂F3的处理土壤养分含量高于其他处理,即内含具特殊功能的芽孢杆菌、丝状真菌、放线菌和酵母菌的秸秆腐解剂F3增加土壤养分的效果最好;相同腐解剂下不同种类秸秆处理的土壤养分含量表现为:WF1CF1,WF2≥CF2,WF3CF3,即由好氧性的多个菌种复合培养而成的秸秆腐解剂F1对小麦秸秆促腐优势最大;F3对玉米秸秆的促腐作用优于F1和F2;富含分解纤维素、半纤维素、木质素和其他生物有机物质的微生物菌群的秸秆腐解剂F2对小麦、玉米秸秆的促腐效果基本相似。     

小麦和玉米秸秆不同还田量下腐解特征及其养分释放规律

通过设置在甘肃省定西市安定区李家堡镇麻子川村尼龙网袋埋土试验,研究玉米、小麦秸秆在10g、30g、50g、70g四个还田量水平(等碳量以小麦含碳量为基准)的腐解特征及其养分释放规律。结果表明:经过100天的腐解,玉米、小麦秸秆的腐解速率均呈现出前期快、后期慢的趋势,玉米秸秆腐解率大于小麦秸秆。就秸秆四个还田量水平来说,还田量为26.23g的玉米秸秆腐解最快,累积腐解率为64.15%,而玉米秸秆还田8.74g处理的腐解最慢。而小麦秸秆还田量为50g的腐解效果较好,10g还田量水平下的腐解率最小。因此,玉米秸秆26.23g或小麦秸秆50g还田的腐解效果较好。     

基于熵技术的半干旱地区土壤水分差异性分析

在安家坡流域6 a实测土壤水分数据的基础上,运用熵技术分析法,对农地、苜蓿、沙棘、荒坡4种不同土地利用下的土壤水分时空变异规律进行了分析。结果显示：土壤水分信息熵效用价值均体现自上而下不断减少的规律,浅层土壤水分信息熵效用价值最大;不同植被覆盖形式下土壤水分信息熵效用价值体现为:荒坡＞沙棘＞农地＞苜蓿,并在60 cm和80 cm深处出现2个土壤水分信息熵增减的突变点;除沙棘灌丛外,7-8月土壤水分环境内部信息熵剧增,信息熵效用价值最低,土壤热容量急剧减少,从而影响到植物的正常生长。     

地表覆盖对旱作玉米农田土壤氮素矿化的影响

采用树脂芯方法研究了黄土高原旱作农田秸秆覆盖和地膜覆盖对0~20 cm土层土壤氮素净矿化的影响。结果表明:不覆盖(对照)、秸秆覆盖和地膜覆盖3个处理在玉米生育前期(播前~六叶期)表现为土壤氮素净固持,净固持量分别为53.7、52.7、56.7 mg·kg~(-1),六叶期之后表现为氮素净矿化,净矿化量分别为26.3、31.8、13.7mg·kg~(-1);综合两个生育阶段从全生育期看,3个处理土壤氮素矿化均表现为净固持,矿质氮净固持量分别为27.4,20.9 mg·kg~(-1)和43.0 mg·kg~(-1)。从不同覆盖处理看,秸秆覆盖会显著增加土壤氮素净矿化量和氮净矿化速率,地膜覆盖虽然有利于增加土壤温度和水分含量,但并没有显著改变土壤氮净矿化量和氮净矿化速率,这一结果间接证明地膜覆盖并不会显著影响土壤有机质矿化。研究还发现,在本试验条件下当田间土壤温度在22℃~25℃、土壤含水量在20%左右时有利于土壤氮素矿化,该条件下净矿化速率较高,且干湿交替有利于矿化。     

玉米秸秆腐解过程物质组成及胡敏酸的动态变化Ⅰ.物质组成的动态变化

采用恒温培养试验，利用植物化学组成系统分析法，对玉米秸秆腐解过程物质组成的动态变化进行了研究。结果表明，随腐解进行，腐解物中木质素、全氮以及灰分的含量逐渐增加；水溶性物质的含量在210d以前逐渐减小，210d以后也有所增加；苯醇溶性物质、纤维素和全碳的含量逐渐减小。腐解过程木质素、纤维素、全碳的总量均呈下降趋势，其分解率与腐解时间的关系可用指数方程来描述。同一腐解期，分解率的大小顺序是纤维素＞全碳＞木质素。腐解过程灰分的总量基本不变，全氮量略有减小。     

冬春季植被残体覆盖对内蒙古河套地区盐碱土盐分的影响

春季是内蒙古河套地区土壤返盐和积盐最严重的季节。本研究在内蒙古河套地区典型盐渍化土壤上设置田间试验,比较紫花苜蓿、羊草、碱茅、柳枝稷、草木樨、猪毛菜和燕麦植株残体冬春季地表覆盖下,表层土壤pH及盐分含量的差异,以期筛选出合适的冬春季植被。结果表明,冬春季植被残体地表覆盖抑盐效果明显,表层土壤EC值降低了42%~73%,平均为61%,这可能是由于Na~+、K~+、Ca~(2+)、Mg~(2+)及Cl~-含量降低所致;但土壤pH值、CO_3~(2-)和HCO~(3-)含量有所升高。总体来看,多年生植被残体覆盖抑制盐分表聚的效果更好一些,其中紫花苜蓿、羊草和柳枝稷,较适于用作本地区冬春季地表覆盖植被。     

干旱荒漠条件下残茬分解特征和养分释放的研究

以大豆秆为材料研究了荒漠生态条件下残茬的腐解率、腐解物的有机C、N和K的含量、养分释放率和C/N比的变化。结果表明:残茬的累积腐解率和有机C的分解率随腐解时间的延长呈上升的趋势,0～1.5个月和1.5～3个月残茬腐解率分别达19.7%和18.5%,0～1.5个月和1.5～3个月残茬有机C的分解率均为19.2%;腐解残留物的有机C、N和K的含量存在不同的变化,有机C的含量变化不大,N的含量则是先逐渐上升,6个月后基本不变,K的含量前1.5个月迅速下降,1.5～3个月缓慢下降,然后基本不变;整个腐解过程是N的固定过程,N的释放量和释放率均为负值,K的释放集中在前1.5个月,释放率达75.8%;腐解残留物的C/N比先迅速下降,6个月后基本不变,最终为35.9。     

林隙对黄土高原马栏林区优势种更新的影响

林隙对森林的结构和动态具有重要的影响。黄土高原马栏林区主要群落类型中,对优势种辽东栎(Quercus liaotungensis)、油松(Pinus tabulaeformis)不同大小林隙内的幼苗和幼树进行统计计算,并与林冠下进行对比分析。结果表明:两个优势种存在不同的更新策略,即辽东栎主要通过高萌发量来维持其种群的更新,而油松则是通过降低幼苗到幼树过程中的死亡率来维持其种群的更新;林隙面积在20~40m²时油松的自然更新情况最好,而辽东栎在不同大小林隙中的自然更新情况较为复杂;适当的林隙干扰总体上促进了该地区优势种的自然更新,林隙对其更新的促进机制各异;在林隙干扰下,辽东栎和油松在各自占优势群落(辽东栎林和油松林)中的优势地位均没有被对方取代的趋势,所以辽东栎林和油松林会作为该地区的顶级群落和亚顶级群落而长期存在。     

吴起县退耕还林后主要植被类型土壤质量评价

为明确吴起县退耕还林后形成的主要植被类型土壤质量状况,文中以吴起县王洼子典型退耕植被作为研究对象,对比分析不同植被类型土壤理化性质差异,并综合主成分分析法、敏感性以及相关性分析法,建立了研究区土壤质量评价指标最小数据集。结果表明:1)不同植被类型间土壤物理、化学性质差异显著(P<0.05);山桃×沙棘混交林在土壤孔隙度、持水性以及有机碳含量方面表现较优;刺槐林在土壤pH和电导率方面表现较优;沙棘林、柠条林在富集氮、磷、钾元素方面优势明显;草地土壤指标整体表现较差。2)适用于研究区不同植被类型土壤质量评价的最小数据集指标为土壤有机碳含量、毛管持水量、电导率和有效磷。3)不同植被类型均在不同程度上有效提高土壤质量,但研究区土壤质量指数整体仍较低,其中山桃×沙棘混交林对土壤质量提升效果最好,其次为灌木林(柠条、沙棘),乔木林(刺槐、杜梨、山桃)和草地。因此,研究区在今后进行低效林改造、林分结构调整与植被恢复重建等林业生态工程时,优先选择以沙棘、柠条为主的灌木林或者小乔木与灌木相结合的混交林(山桃×沙棘混交林)。     

Impacts of land disturbance and restoration on runoff production and sediment yield in the Chinese Loess Plateau

Land disturbance and land restoration are important factors influencing runoff production and sediment yield in the semi-arid loess regions of China. This study compared the runoff production and sediment yield during the early stage after land disturbance(ESLD) with those during restoring stage after land disturbance(RSLD). Grey relational analysis was used to analyse the importance of each one of the influencing factors(vegetation, rainfall, soil and topography) in affecting the runoff production and sediment yield. Our results showed that during ESLD, topography was the most critical factor controlling the runoff production, while soil was the most important factor controlling the sediment yield. During RSLD, vegetation was more important in affecting runoff production, while rainfall was more important in affecting sediment yield. In additional, this study demonstrated that both the runoff production and the sediment yield can be effectively reduced by restoring vegetation on severely-disturbed lands, thus providing an important theoretical basis for better implementations of the Grain for Green Program. Our results revealed that the vegetation types of Hippophae rhamnoides+Pinus tabulaeformis and H. rhamnoides are better plant selections for land restoration in this area, especially for relatively gentle slopes(i.e., less than 20 degrees).     

Contrasting effects of nitrogen addition on litter decomposition in forests and grasslands in China

Nitrogen (N) addition has profound impacts on litter-mediated nutrient cycling. Numerous studies have reported different effects of N addition on litter decomposition, exhibiting positive, negative, or neutral effects. Previous meta-analysis of litter decomposition under N addition was mainly based on a small number of samples to allow comparisons among ecosystem types. This study presents the results of a meta-analysis incorporating data from 53 published studies (including 617 observations) across forests, grasslands, wetlands, and croplands in China, to investigate how environmental and experimental factors impact the effects of N addition on litter decomposition. Averaged across all of the studies, N addition significantly slows litter decomposition by 7.02%. Considering ecosystem types, N addition significantly accelerates litter decomposition by 3.70% and 11.22% in grasslands and wetlands, respectively, clearly inhibits litter decomposition by 14.53% in forests, and has no significant effects on litter decomposition in croplands. Regarding the accelerated litter decomposition rate in grasslands due to N addition, litter decomposition rate increases slightly with increasing rates of N addition. However, N addition slows litter decomposition in forests, but litter decomposition is at a significantly increasing rate with increasing amounts of N addition. The responses of litter decomposition to N addition are also influenced by the forms of N addition, experiential duration of N addition, humidity index, litter quality, and soil pH. In summary, N addition alters litter decomposition rate, but the direction and magnitude of the response are affected by the forms of N addition, the rate of N addition, ambient N deposition, experimental duration, and climate factors. Our study highlights the contrasting effects of N addition on litter decomposition in forests and grasslands. This finding could be used in biogeochemical models to better evaluate ecosystem carbon cycling under increasing N deposition due to the differential responses of litter decomposition to N addition rates and ecosystem types.     

青海湖东沙地不同植被恢复措施下土壤水分变化特征

土壤水分是沙地植被格局和过程改变的主要驱动力,也是干旱半干旱区植物生长最大的限制因子。沙漠地区的土壤水分表现出明显的空间异质性。以高寒半干旱沙地青海湖东沙地为研究区,以栽植人工固沙植物(小叶杨、樟子松、沙棘和乌柳)的沙丘和自然固定沙丘(沙蒿为优势种)作为研究样地,探讨不同固沙植物影响下的沙丘不同地貌部位土壤水分变化特征。结果表明:(1)土壤水分的季节变化受降水、植被蒸腾作用和地表蒸发的共同影响,不同物种的分布模式具有差异性,但都表现为7月的土壤含水量最高。(2)同一植物在不同地貌部位的土壤含水量具有差异性,小叶杨在迎风坡最高,樟子松、沙棘和乌柳在背风坡最高,而沙蒿在丘顶最高,但只有乌柳的土壤含水量在沙丘地貌部位间的差异明显(P<0.05)。不同植物在同一地貌部位的土壤含水量也具有差异性,迎风坡樟子松的土壤含水量最小,只有1.81%,而沙蒿的土壤含水量能达到3.48%。丘顶处乌柳的土壤含水量仅为1.82%,而沙蒿可达3.58%。背风坡处的土壤含水量相差不大,乌柳最大为3.41%。(3)土壤水分随着土层深度的变化模式不同,土壤含水量整体表现为10~20 cm处最高。不同植物的土壤水分的垂直分布具有差异性,小叶杨和樟子松下方的土壤含水量随着土层深度的增加而降低,沙棘和沙蒿表现为120 cm土层深度内无明显变化,而乌柳下方的土壤含水量随着土层深度的变化在各地貌部位不同,具体表现为迎风坡无明显变化、丘顶降低和背风坡增加的趋势。土壤水分在高寒半干旱沙地不同植被恢复措施下的分布除受到降水、土壤分布、物种类型、植物根系分布的影响之外,还与沙丘微地貌形态具有一定的相关性。     

典型荒漠植物凋落物分解及养分动态研究

采用分解网袋法,对古尔班通古特沙漠南缘粗柄独尾草(Eremurus inderiensis)、尖喙牻牛儿苗(Erodium oxyrrhynchum)和沙漠绢蒿(Seriphidium santolinum)3种荒漠植物叶、茎和根的分解、养分释放特性进行了研究。结果表明：叶片、茎、根系的质量损失过程均符合指数衰减模型。经过364 d的分解,粗柄独尾草叶、粗柄独尾草根、尖喙牻牛儿苗叶、尖喙牻牛儿苗茎、尖喙牻牛儿苗根、沙漠绢蒿茎、沙漠绢蒿根的失重率分别为41.96%、81.94%、42.18%、29.32%、47.02%、20.66%和20.71%;3种植物根、茎、叶的分解速率存在显著差异,分解速率依次为：粗柄独尾草根>叶;尖喙牻牛儿苗根>叶>茎;沙漠绢蒿根>茎。在整个分解过程中,N和P含量总的趋势表现为释放,叶、根凋落物质量损失与初始N、P含量显著负相关,非生物因素对其分解有重要影响。     

晋北黄土丘陵区不同林草措施的蓄水保土和土壤水分效应研究

以设在山西省阳高县的大型径流观测场为依托,以2005-2009年的野外实测数据为依据,研究了晋北黄土丘陵区人工植被与鱼鳞坑配合的蓄水保土及土壤水分效应,并与荒坡、苜蓿地进行了对比。结果表明:在观测的5年内,柠条、沙棘、油松的蓄水保土能力随种植年限延长无明显增加趋势,但鱼鳞坑的蓄水能力和保土能力分别高达84.7%～96.0%和95.2%～99.7%;荒坡和苜蓿(Medicago sativa)第一年和第二年的蓄水保土能力较差,第三年和第四年随植被盖度增加能力急剧增强,第四年蓄水能力分别达82.8%和91.2%,保土能力达97.0%和98.0%;土壤水份分析结果表明:不同小区4～9月土壤水分变异系数为7.0%～19.1%,油松区变异系数最大,其次为沙棘、苜蓿和柠条区,荒坡区和裸坡区变异较小,不同小区土壤水分亏缺率为23.98%～52.66%,亏缺顺序为柠条区>苜蓿区>油松区>沙棘区>荒坡区>裸坡区;林草植被有效地减少了水土流失,亦增加了土壤水分的变异及亏缺程度,应注意林草植被的合理选择和配置。     

Hydrosoil residues and Hydrilla verticillata control in a central florida lake using fluridone

Fluridone was applied to a 98-8-ha lake in Orange County, Florida, USA, in five different treatment plots between October 1982 and February 1983 to control a severe infestation of Hydrilla verticillata. Hydrosoil residues and submersed aquatic plant biomass were monitored within the lake. Fluridone did not affect the submersed vegetation during the 4-month fall-winter treatment period. As water temperatures increased during spring, Hydrilla biomass declined at an average of 0.178 kg m^?2 per month. By summer (192 days after last treatment), the target species could not be found within the lake. Fluridone residues were detected in the hydrosoil immediately following treatments and generally peaked coinciding with the decline in aquatic plant biomass. The maximum fluridone detected in the hydrosoil was only 5% of the 2.25 kg ha^?1 applied, and this amount was obtained from outside of a treatment area. Residue concentrations were highly variable between sampling sites and sampling periods and unexpectedly increased 14 months after treatment. Winter-killed marginal vegetation is a possible source of this increase. Detectable concentrations of fluridone, and vegetation control, persisted for a total of 86 weeks from the date of the last treatment and non-detectable residues may have persisted after 86 weeks. This study indicates that a lower application rate might have provided adequate control of Hydrilla and possibly decreased residue concentrations in non-target areas.     

氯氰菊酯在茼蒿和油麦菜上的残留行为研究

为考察氯氰菊酯在茼蒿和油麦菜上的残留行为,于2016年在山西、山东、天津、安徽、云南和河南进行了氯氰菊酯在茼蒿和油麦菜上的规范残留田间试验。两种作物均包括6地的最终残留量试验和1地的消解动态试验。按照现行的蔬菜中拟除虫菊酯类农药残留测定的国家标准方法对样品进行检测,对方法的有效性进行了评价。田间试验结果表明:氯氰菊酯在茼蒿和油麦菜上的消解动态均符合准一级动力学方程,消解半衰期分别为3.2 d和1.8 d。最后一次施药3、5和7 d后,氯氰菊酯在茼蒿上的残留中值分别为1.64、1.19和0.89 mg/kg,在油麦菜上的残留中值分别为0.84、0.50和0.28 mg/kg。结合不同试验点试验期间昼夜平均气温发现,气温对氯氰菊酯在茼蒿和油麦菜上的残留量有明显影响。施药期间较低的气温下,氯氰菊酯在茼蒿和油麦菜上消解缓慢,残留风险明显增大。建议在实际生产中遇到低温天气应适当延长采收间隔期,另外在开展农药残留田间试验时应重视气象条件对残留试验结果的影响。     

A spatial-explicit dynamic vegetation model that couples carbon,water,and nitrogen processes for arid and semiarid ecosystems

Arid and semiarid ecosystems,or dryland,are important to global biogeochemical cycles.Dryland's community structure and vegetation dynamics as well as biogeochemical cycles are sensitive to changes in climate and atmospheric composition.Vegetation dynamic models has been applied in global change studies,but the complex interactions among the carbon(C),water,and nitrogen(N) cycles have not been adequately addressed in the current models.In this study,a process-based vegetation dynamic model was developed to study the responses of dryland ecosystems to environmental changes,emphasizing on the interactions among the C,water,and N processes.To address the interactions between the C and water processes,it not only considers the effects of annual precipitation on vegetation distribution and soil moisture on organic matter(SOM) decomposition,but also explicitly models root competition for water and the water compensation processes.To address the interactions between C and N processes,it models the soil inorganic mater processes,such as N mineralization/immobilization,denitrification/nitrification,and N leaching,as well as the root competition for soil N.The model was parameterized for major plant functional types and evaluated against field observations.     

黄土丘陵沟壑区乔灌木植物系数计算与适应性评价

利用长期定位试验资料,研究了黄土高原丘陵沟壑区乔木和灌木植物系数的计算方法,比较了两种代表性乔木(榆树和小叶杨)和两种代表性灌木(柠条和沙棘)的实际蒸散量和生育期土壤平均含水量的差异,分析了土壤含水量变化对植物根系吸水和土壤水分有效性的影响。结果发现:该地区灌木的实际蒸散量小于乔木,但同类植物的实际蒸散量没有显著差异;土壤含水量柠条最高,沙棘最低;榆树植物系数最小,柠条其次,沙棘最大,但榆树和小叶杨的土壤水分有效性高,耗水量大,所以灌木较适于该区生长。