Effects Of N And P Addition On Soil Nutrient In A Subtropical Evergreen Broad-leaved Forest

Soil is one of the important environment factors, and the basis for plant survival.Therefore, soil is an important part of forest ecosystem research. On the one hand, theforest soil provides the necessary material base for the existence and development offorest vegetation; On the other hand, the emergence and its succession of forestvegetation, in turn, can affect the soil formation and development. As the populationincreases, economic development and environmental change, land degradation andpollution become very serious. Soil quality is one of the important factors forsustainable development of the global biosphere, and is the evaluation and judgmentcriteria of ecological environment, soil management and sustainable land use. Soilnutrient conditions affect tree growth, and determine the productivity of forestecosystems.In the case of high nitrogen （N） deposition under the background of globalization,evaluation of the effect of nitrogen deposition in forest ecosystems and its feedback tomake reasonable economic development strategy and plan of forest resources andenvironmental management has important theoretical value and practical significance.Therefore, six permanent plots were established in a subtropical evergreenbroad-leaved forest in Chawan Natural Reserve, southern Anhui, in January2011. Afertilization experiment was conducted. The experimental design included threetreatments with two replications: the control, high N (100kg N hm-2a^-1) and high N+phosphorus (100kg N hm-2a^-1+50kg P hm-2a^-1). The objective of the study is todetermine the effects of N addition on soil nutrient status and to reveal the responsivemechanism of soil nutrient dynamics to nitrogen deposition in subtropical evergreenbroad-leaved forest. The results obtained are as follows.Before nutrient additions, the pH （H2O） for0^-10cm soil layers averaged4.28, andpH （KCl）3.34. The mean EC was200.47μS·cm^-1. The mean concentrations of totalnitrogen was3.13g·kg^-1, total potassium9.52g·kg^-1, total calcium83.22g·kg^-1, totalmagnesium1.70g·kg^-1, total phosphorus176.03mg·kg^-1. No significant differencesappeared among the different treatment stands （p>0.05）.After the nutrient additions, the concentrations of NH4+-N in0^-10cm soil layerwere highest in June2012(11.05mg·kg^-1) and lowest in December2011(3.60mg·kg^-1) for the control （CK）; whili highest in October2011(14.64mg·kg^-1) andlowest in September2011(4.90mg·kg^-1) for the nitrogen （N） addition, and highest in August2011(17.24mg·kg^-1) and lowest in September2011(4.90mg·kg^-1) fornitrogen and phosphorus （N+P） addition. In the10-20cm soil layer, the NH4+-Nconcentrations were highest in August2011(19.16mg·kg^-1) and lowest in theDecember2011(2.50mg·kg^-1) for CK; but highest in August2011(11.67mg·kg^-1)and lowest in July2011(3.41mg·kg^-1) for N addition; and highest in August2011(15.45mg·kg^-1) and lowest in July2011(2.97mg·kg^-1) for N+P addition.Concentrations of NO-3-N in0^-10cm soil layer were highest in February2012(1.65mg·kg^-1) and lowest in the December2011(0.17mg·kg^-1) for CK; while highestin October of2011(22.51mg·kg^-1) and lowest in April2012(0.17mg·kg^-1) for Naddition; and highest in October of2011(7.14mg·kg^-1) and lowest in April2012,0.18mg·kg^-1) for N+P addition. In the10-20cm soil layer, the NO-3-N concentrations werehighest in July2011(1.43mg·kg^-1) and lowest in October of2011(0.35mg·kg^-1) forCK, highest in October of2011(10.08mg·kg^-1) and lowest in April2012(0.18mg·kg^-1) for N addition; while highest in October of2011(4.11mg·kg^-1) and lowest inApril2012,0.20mg·kg^-1) for N+P addition. Significant differences were appearedbetween treatments and control （p <0.05）, but no significant differences was appearedbetween the treatments （p>0.05）.Concentrations of available P （AP） in0^-10cm soil layer were highest in June2012(5.71mg·kg^-1) and lowest in the December2011(0.46mg·kg^-1) for CK; highestin September2011(2.82mg·kg^-1) and lowest in the December2011(1.41mg·kg^-1) forN addition; highest in December2011(3.81mg·kg^-1) and lowest in the December2011(0.37mg·kg^-1) for N+P addition. In10-20cm soil layer, AP concentrations werehighest in May (1.13mg·kg^-1) and lowest in the December2011(0.58mg·kg^-1) forCK; highest (3.96mg·kg^-1) in April2012and lowest in July2011(1.08mg·kg^-1) for Naddition; highest levels in April2012(3.34mg·kg^-1) and lowest in July2011(0.92mg·kg^-1) for N+P addition.. No significant difference appeared between CK and Naddition （p>0.05）, while significant differences appeared between CK and N+Paddition addition （p <0.05）.The contents of dissolved organic carbon （DOC） in0^-10cm soil layer werehighest in August2011(368.24mg kg^-1), lowest in October of2011(118.37mg·kg^-1)for CK; and highest in August2011(391.16mg·kg^-1) and lowest in June2012(84.32mg·kg^-1) for N addition; while highest in August2011(381.43mg·kg^-1) and lowest inJune2012(92.71mg·kg^-1) for N+P addition.The results from the in-situ incubation experiment showed that the rate of ammonification （Rna） in0^-10cm soil layer was highest (556.87μg·kg^-1·d^-1) fromJune to July2012and lowest (-230.82μg·kg^-1·d^-1) from August to September2011;for nitrification rate （Rnn） were671.50μg·kg^-1·d^-1from June to July2012and^-18.67μg·kg^-1·d^-1from February to April2012; for mineralization rate （Rnm） were1228.37μg·kg^-1·d^-11from June to July2012and^-163.31μg·kg^-1·d^-1from August to September2011. And in10-20cm soil layer, the highest Rna was244.31μg·kg^-1·d^-1fromFebruary to April2012and the lowest-467.57μg·kg^-1·d^-1from August to September2011; the highest Rnn was201.13μg·kg^-1·d^-1from June to July2012and the lowest-8.30μg·kg^-1·d^-1from February to April2012;the highest Rnm was392.73μg·kg^-1·d^-1from June to July2012and the lowest-438.28from August to September2011.In the treatment of N addition, the Rna in0^-10cm soil layer was highest (583.64μg·kg^-1·d^-1) from June to July2012and lowest (-233.79μg·kg^-1·d^-1) from August toSeptember2011; for Rnn were687.39μg·kg^-1·d^-1from June to July2012) and-343.87μg·kg^-1·d^-1from October to December2011; for Rnm were1271.03μg·kg^-1·d^-11from June to July2012and-278.10μg·kg^-1·d^-1from October to December2011. And in10-20cm soil layer, the highest Rna was285.31μg·kg^-1·d^-1from June toJuly2012and the lowest-264.72μg·kg^-1·d^-1from August to September2011; thehighest Rnn was177.65μg·kg^-1·d^-1from June to July2012and the lowest-89.26μg·kg^-1·d^-1from October to December2011; the highest Rnm was462.97μg·kg^-1·d^-1from June to July2012and the lowest^-190.86from October to December2011.In the treatment of N+P addition, the Rna in0^-10cm soil layer was highest(379.83μg·kg^-1·d^-1) from September to October2011and lowest (-404.18μg·kg^-1·d^-1)from August to September2011; for Rnn were676.65μg·kg^-1·d^-1from June to July2012and-64.36μg·kg^-1·d^-1from October to December2011; for Rnm were877.39μg·kg^-1·d^-1from June to July2012and-407.86μg·kg^-1·d^-1from August to September2011. And in10-20cm soil layer, the highest Rna was162.31μg·kg^-1·d^-1from June toJuly2012and the lowest-417.96μg·kg^-1·d^-1from August to September2011; thehighest Rnn was285.00μg·kg^-1·d^-1from September to October2011and the lowest-417.96μg·kg^-1·d^-1from August to September2011; the highest Rnm was351.21μg·kg^-1·d^-1from June to July2012and the lowest-425.14μg·kg^-1·d^-1from August toSeptember2011.The results show that the inorganic nitrogen concentrations in the surface soillayer one month after the treatments were higher than than for the control, withmore sensitive to nutrient additions in0^-10cm soil layer than in10-20cm soil layer. This indicates that short-term （1-2years） N addition can significantly affect soil Nmineralization, particularly for the surface soil. The N and N+P additions made asignificant increase in concentrations of NH4+-N and NO-3-N in the two soil layers,while no significant difference occurred between the two treatments. The APconcentration is higher for the treatments than for the control. The differences becamegreater as fertilization continued. However, no significant difference occurred for APbetween N addition and control.The rates of ammonification, nitrification and mineralization in0^-10cm and10-20cm soil layers showed a similar seasonal pattern despite the different treatments.The annual mean nitrogen transformation rate is highest in summer and lowest inwinter. The preliminary results of this study showed that the annual averagemineralization rate was dropped by nutrient additions. The N addition resulted indecline of nitrification rate and increase of ammonification rate. However, N+Paddition caused to increase nitrification rate and to decrease ammonification rate. Theeffects of nutrient addition on N dynamics in forest ecosystem need long-termobservation.