Abstract
The fern Dicranopteris dichotoma is an important pioneer species of the understory in Masson pine (Pinus massoniana) forests growing on acidic soils in the subtropical and tropical China. To improve our understanding of the role of D. dichotoma in nitrogen (N) uptake of these forests, a short-term 15N experiment was conducted at mountain ridge (MR, with low N level) and mountain foot (MF, with high N level). We injected 15N tracers as 15NH4, 15NO3 or 15N-glycine into the soil surrounding each plant at both MR and MF sites. Three hours after tracer injection, the fern D. dichotoma took up 15NH4 + significantly faster at MF than at MR, but it showed significantly slower uptake of 15NO3 − at MF than at MR. Consequently, 15NO3 − made greater contribution to the total N uptake (50% to the total N uptake) at MR than at MF, but 15N-glycine only contributed around 11% at both sites. Twenty-four hours after tracer injection, D. dichotoma preferred 15NH4 + (63%) at MR, whereas it preferred 15NO3 − (47%) at MF. We concluded that the D. dichotoma responds distinctly in its uptake pattern for three available N species over temporal and spatial scales, but mainly relies on inorganic N species in the subtropical forest. This suggests that the fern employs different strategies to acquire available N which depends on N levels and time.
Highlights
Nitrogen (N) is a major limiting element in many terrestrial ecosystems [15,32]
N acquisition mechanisms of D. dichotoma remain unknown in these tropical forests, and clarification of D. dichotoma N uptake patterns could improve the mechanistic understanding of its role in these subtropical and tropical forests
Two sites were selected along a mountain slope (Figure 1): one was located at the mountain ridge (MR) and the other was located at the foot of the mountain (MF)
Summary
Nitrogen (N) is a major limiting element in many terrestrial ecosystems [15,32]. In the past three decades a large number of plants have been identified to have the capacity to directly take up organic N, mainly in the form of amino acids from soil solution [3,11,21,22]. Uptake pattern of different N species may be an important mechanism responsible for species coexistence in plant communities[19]. Numerous studies on plant N acquisition of organic and inorganic N species have been conducted in subtropical and tropical forests, most focusing on tree species [1,27,28,29,36,37,38], bryophytes and lichens [6,34] as well as some epiphytes [8,35]. Numerous studies have suggested that Dicranopteris species can influence many ecological processes in these forests, such as soil erosion, nutrient cycling, tree regeneration, and plant community succession [5,25,26,41]. N acquisition mechanisms of D. dichotoma remain unknown in these tropical forests, and clarification of D. dichotoma N uptake patterns could improve the mechanistic understanding of its role in these subtropical and tropical forests
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