Effect Of Experimental Phosphorus Additions And Diversity Of Non-agricultural Plants On Soil Nematode Communities

With the increase of population and large food need, it is very important to improve soil fertility and the grain yield, suppress farmland weeds. Phosphorus is one of the essential elements of crop grow, the fertilizer application has increased rapidly in farmland in recent years. Therefore,plant diversity decline caused by phosphate fertilizer and weeds have impact on soil health, which has become an important topic in ecology research. As the most abundant and diversity invertebrates in soil, nematodes are an important component of the soil biotic community.Furthermore nematode fauna provides a unique assessment to soil biological processes. Therefore soil nematodes are chosen to check biological process as biological indicator.The experiment was investigated by addition of different fertilization and planting non-agricultural plants treatments in outdoor pots and the fertilizer treatment(phosphorus additions) was applied as main factor and kinds of non-agricultural plants treatment as secondary factors. As the first factor, phosphate was divided into control(P-) and adding phosphate fertilizer(P+). There were 36 repeats in each fertilizer treatments. As a second factor, 4 kinds non-agricultural plants were used in the study including 0(NW), 1 kind plant(OW), 2 kinds of plants(TW) and 4 kinds of plants(FW). Soil nematodes were sampled in winter wheat booting stage. The Baermann funnel technique was used to extract soil nematodes. Soil nematodes were identified to genus level. Abundance and richness of soil nematodes, trophic groups, functional group index, ecological index and nematode faunal analysis of soil nematodes were used to evaluate effects of phosphorus additions and diversity of non-agricultural plants on nematode community composition and mechanism. The study would clarify structure of nematode community under phosphorus additions and diversity of non-agricultural plants treatments. The results were as follows:1. A total of 28592 soil nematode individuals were captured, and fell into 2 classes, 7orders, 16 families, 30 genera in the winter wheat booting stage. Soil nematodes comprised 13417 bacteria feeders, 11 genera and 1680 fungi feeders, 2 genera and 11128 plant-parasites, 10 genera,and 2364 omnivore-predator, 7 genera. The dominant genera of soil nematodes were Rhabditis(18%), Pratylenchus(17%) and Tylenchorhynchus(10%). Abundance of soil nematodes was higher in P+ treatment than in P- treatment. Total abundance of soil nematode was the highest in P+ and TW treatment, and in P- and NW treatment. Contrast to P- treatment, total abundance(F=12.513, P=0.001) and total richness(F=14.837, P=0.000) of soil nematodes significantly increased in P+ treatment. The increase value of abundance was 0.574, and the increase value of richness was 2.167. Total abundance and richness of soil nematodes had no significant difference in non-agricultural plant treatment. Total abundance and richness of soil nematodes had also no significant difference under P+ and non-agricultural plants interaction.2. Ecological parameters : In P+ treatment, OP/Pp, H`, SR, E, MI values of soil nematodes increased with non-agricultural plant diversity. H`, E index of soil nematodes showed significant difference in NW treatment and FW treatment. Contrasted to NW, OW and FW treatments, OP/Pp, H`, SR, E, MI indexes of soil nematode, TW non-agricultural plant has the highest value in P- treatment, and abundance of soil nematodes had significant difference. The total number of nematodes, abundance of bacterial feeding nematode, abundance of the plant-parasites feeding nematode and Ba1、Fu2、Pp5、OP5 showed significant difference by measuring double factor variance analysis, and had no apparent different in interaction of P+ and non-agricultural plants treatment. Nematode faunal analysis results showed that enrichment index and structure index of soil nematodes changed between “ 50-100 ” under P+ treatment and non-agricultural plants treatment is located in quadrant B, The results indicated that the soil nutrient content was high and was disturbed less. Food webs were stable and mature in the soil.3. Soil physical and chemical properties were used to assess soil nematodes by using correlation and regression analysis. The results showed that soil organic carbon and abundance of total nematode(R2=0.293, P<0.001), abundance of bacteria-feeding nematodes(R2=0.259,P<0.001), abundance of plant-parasites nematodes(R2=0.272, P<0.001), plant-parasites functional groups of cp-5 value(R2=0.259, P<0.001), enrichment index(R2=0.134, P<0.001) had significantly correlated. While organic carbon in the soil had significant negative correlation with maturity index(R2=0.159, P<0.001) and channel index(R2=0.130, P<0.001) of free-living nematodes. Available phosphorus in soil had significantly positively correlation with total abundance(R2=0.180, P<0.001) of nematode, abundance of bacteria-feeding nematodes(R2=0.222,P<0.001), abundance of plant-parasites nematodes(R2=0.148, P<0.001) and enrichment index(R2=0.151, P<0.001). There were significantly negative correlation between available phosphorus and total nematode richness(R2=0.122, P<0.05), maturity index(R2=0.152, P<0.001) o free-living nematode, the structure index(R2=0.122, P<0.05), the channel index(R2= 0.155, P<0.001).Ammonium nitrogen had significant positively correlation with structure index(R2=0.087,P<0.05), the channel index(R2=0.130, P<0.05). But Ammonium nitrogen had significantly negatively correlation with total nematodes abundance(R2=0.145, P<0.05), abundance of bacteria-feeding nematodes(R2=0.167, P<0.001), abundance of plant-parasites nematodes(R2=0.125, P<0.05), total richness of nematodes(R2=0.160, P<0.001), evenness index(R2=0.041,P<0.05), enrichment index(R2=0.153, P<0.001).To sum up, application of phosphate fertilizer can increase the soil nutrient content and soil nematode abundance, change organic matter decomposition pathway and reduce the rare species. Negative effects on soil nematodes community by applying fertilizer were slowed down under increasing the non-agricultural plant diversity. Food webs of soil nematodes become complicated and stable. The results can provide a theoretical base for fertilization and weeding measures, biodiversity conservation and soil health in farmland.