Low Nitrogen Retention in Soil and Litter under Conditions without Plants in a Subtropical Pine Plantation

Abstract

Soil acts as a major sink for added nitrogen (N) in forests, but it remains unclear about the capacity of soil to immobilize N under conditions without plant roots and whether added N interacts with ecosystem N to affect N retention. We added 15 NH4 15 NO3 to in situ soil columns (with leaching) and leaf litter (without leaching) of two tree species in a subtropical Pinus elliottii plantation. Soil and litter were collected three or eight months after N addition to measure concentrations of indigenous and exogenous N. About 70% of exogenous N was retained in soil three months after N addition, of which 65.9% were in inorganic forms. Eight months after N addition, 16.0% of exogenous N was retained in soil and 9.8%-13.6% was immobilized in litter. N addition increased the mineral release and nitrification of soil indigenous N. Loss of litter indigenous N was also increased by N addition. Our results suggest that N deposition on lands with low root activities or low soil carbon (C) OPEN ACCESSForests 2015, 6 2388 contents may lead to increased N output due to low N immobilization. Moreover, the effects of added N on ecosystem indigenous N may decrease the capacity of soil and litter in N retention.

Effects of Experimental Nitrogen Addition on Nutrients and Nonstructural Carbohydrates of Dominant Understory Plants in a Chinese Fir Plantation

“…The area is a typical red soil hilly region with a subtropical moist monsoon climate. The soil belongs to the typical Hapludult Ultisols with 68% sand and 15% clay [20]. The month average temperatures range from 6.5 • C in January to 29.7 • C in July, and a mean annual temperature is 18 • C. The annual precipitation ranges from 945 to 2144 mm, with an average of 1500 mm [21].…”