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Understanding the role of biodiversity (B) in maintaining ecosystem function (EF) is a foundational scientific goal with applications for resource management and conservation. Two main hypotheses have emerged that address B-EF relationships: niche complementarity (NC) and the mass-ratio (MR) effect. We tested the relative importance of these hypotheses in a subtropical old-growth forest on the island nation of Taiwan for two EFs: aboveground biomass (ABG) and coarse woody productivity (CWP). Functional dispersion (FDis) of eight plant functional traits was used to evaluate complementarity of resource use. Under the NC hypothesis, EF will be positively correlated with FDis. Under the MR hypothesis, EF will be negatively correlated with FDis and will be significantly influenced by community-weighted mean (CWM) trait values. We used path analysis to assess how these two processes (NC and MR) directly influence EF and may contribute indirectly to EF via their influence on canopy packing (stem density). Our results indicate that decreasing functional diversity and a significant influence of CWM traits were linked to increasing AGB for all eight traits in this forest supporting the MR hypothesis. Interestingly, CWP was primarily influenced by NC and MR indirectly via their influence on canopy packing. Maximum height explained more of the variation in both AGB and CWP than any of the other plant functional traits. Together, our results suggest that multiple mechanisms operate simultaneously to influence EF, and understanding their relative importance will help to elucidate the role of biodiversity in maintaining ecosystem function.

The Coastal Range in eastern Taiwan is characterized by rapid uplift at a rate of about 5 mm [yr-sup.1] because of active arc-continent collision since the Mio-Pliocene. The Coastal Range includes three main levels of Holocene marine terraces, labeled the first, second, and third levels descending to the coast. The soils that have developed on the terraces provide a chronosequence for pedogenic studies. Thirteen soil pedons formed from conglomerate associated with tuff were sampled along three transects in the central and southern part of the eastern coast of Taiwan near the localities of Chang-Bin, Cheng-Gong, and Du-Lan. The soils of the oldest terrace (first level) are mainly Typic Hapluderts with one Typic Hapludoll; the soils of the intermediate terrace (second level) are Vertic or Typic Hapludolls; and the soils of the youngest terrace (third level) are Typic Udipsamments. The degree of development of these soils can be determined from horizon index (HI), weighted profile development index (WPDI), weighted mean profile (WMP) clay, WMP silt, WMP sand, and WMP cation exchange capacity with correlation coefficients (r) >0.6 by linear or logarithmic functions. Comparisons of the chronofunctions based on WMP clay data in subtropical and Mediterranean climates suggest that climatic conditions not only control weathering intensity but also influence rates of soil development. The pedogenic evidence in this study supports the correlation of terraces suggested by previous geomorphic and tectonic studies. The anomalous, relatively weaker degree of soil development on the oldest terrace at Du-Lan supports the conclusion that uplift rates in the Du-Lan area are greater than at Chang-Bin and Cheng-Gong. Abbreviations: cal., calibrated; HI, horizon index; OC, organic carbon; WMP, weighted mean profile; WPDI, weighted profile development index; XRD, x-ray diffraction. doi: 10.2136/sssaj2009.0276

PAce (Oryza sativa L.)-growing soils with plinthite and abundant ferromanganiferous nodules ([greater than or equal to] 60 g [kg.sup.-1]) were selected to evaluate the formation mechanisms of ferromanganiferous nodules and to determine the relationships among the characteristics of ferromanganiferous nodules tinder different moisture regimes in soils. Depth to water table, water potential, and redox potential (Eh) were monitored at different soil depths during 2004 and 2005. The results show that the greatest quantity of ferromanganiferous nodules (91-492 g [kg.sup.-1]) were found in plinthic horizons, which had reducing conditions for a moderate amount of time (about 47% of the year). This was especially true for nodules >20 mm in diameter. Micromorphological observation of ferromanganiferous nodules revealed that co-presentation of secondary Fe and Mn oxides and oriented clay is more apparent in coarser nodules than finer nodules. Based on the micromorphological observation, we deduced that nodules were formed when Mn(II) first precipitated within micropores or coated the coarse nuclear grain surface. Later, reduced Fe, Mn, and illuvial clay continued reoxidizing and precipitating on the initial Mn nodules, which then grew to a larger size. The Fe activity ratio (oxalate- to dithionite-extractable Fe) is suggested as a good index for prediction of the annual duration of reducing conditions in the soils examined in this study'. Furthermore, the dithionite-extractable Mn/Fe ratio in nodules is a good indicator for prediction of the soil depths where the water table fluctuated, because Mn accumulated and was well crystallized at these depths. Abbreviations: DCB, dithionitc--citrate--bicarbonate. doi: 10.2136/sssaj2009.0020