Greenfall litter decomposition of three common species in the northern Chihuahuan Desert, 2010-2012

Soil organic carbon (SOC) is derived primarily from the decomposition
of plant biomass. Animals that create greenfall, or green leaf litter,
influence SOC dynamics by altering the phenological condition and,
therefore, nutrient quality of plant litter. Animals that transport
greenfall to a microsite with different microhabitat conditions from
those where senesced litter would typically be found also influence
SOC dynamics by altering the prevalence of various decomposition
drivers. Microsite differences are particularly pronounced in arid and
semi-arid ecosystems with heterogeneous vegetation cover. We
investigated differences in decomposition between greenfall and
senesced litter of three common Chihuahuan Desert plants from which
animals frequently generate greenfall (Larrea tridentata, Sporobolus
flexuosus, Yucca elata), using a litterbag study to quantify
differences in mass, carbon (C), and nitrogen (N) losses between green
and senesced leaves placed in shrub intercanopy and subcanopy
microsites in a desert shrubland. We hypothesized that decomposition
would be more rapid in 1) greenfall than naturally senesced litter,
because of the higher nutrient concentration in green than senesced
leaves, and 2) in intercanopy than shrub subcanopy microsites, because
of increased exposure to decomposition drivers like soil-litter mixing
and photodegradation in the less vegetated open area between shrub
canopies. Using a litterbag study, we quantified differences in litter
mass, C, and N losses between green and senesced leaves placed in
shrub subcanopy and intercanopy (open) microsites. Measured variables
include litter mass and litter ash, carbon, and nitrogen content. We
found that there were significant differences in the nutrient
concentration of green and senesced leaves of the same species, and
that both litter condition and microsite affected decomposition rate.
For two of the three litter species, greenfall decomposed more rapidly
than senesced litter, and for all three species litter in intercanopy
microsites decomposed more rapidly than in subcanopy microsites. Our
results support that the creation and translocation of greenfall by
animals is an important mechanism regulating the speed of
decomposition and the transfer of C and nutrients from plant biomass
into the soil.

土壤有机碳（Soil Organic Carbon, SOC）主要来源于植物生物质的分解过程。产生鲜叶凋落物（greenfall）的动物，可通过改变植物凋落物的物候状态进而调控其养分品质，以此影响土壤有机碳动态。将鲜叶凋落物搬运至与自然衰老凋落物通常所处微生境不同的微位点的动物，也会通过改变各类分解驱动因子的丰度，进而影响土壤有机碳动态。微位点差异在植被覆盖异质性较强的干旱与半干旱生态系统中尤为显著。
本研究针对奇瓦瓦沙漠中三种常见的、动物常从中产生鲜叶凋落物的植物（Larrea tridentata、Sporobolus flexuosus、Yucca elata），通过凋落物袋实验，量化放置于荒漠灌丛冠层间与冠层下微位点的鲜叶与衰老叶片的质量、碳（C）与氮（N）流失量差异，以此对比二者的分解过程差异。本研究提出两项假设：其一，鲜叶凋落物的分解速率快于自然衰老凋落物，因鲜叶养分浓度高于衰老叶片；其二，冠层间微位点的凋落物分解速率快于冠层下微位点，因灌丛冠层间植被覆盖度更低的开阔区域，土壤-凋落物混合、光降解等分解驱动因子的作用更强。
本研究通过凋落物袋实验，量化了放置于灌丛冠层下与冠层间（开阔）微位点的鲜叶与衰老叶片的凋落物质量、碳与氮流失量差异。测定指标包括凋落物质量，以及凋落物灰分、碳与氮含量。研究结果显示，同一物种的鲜叶与衰老叶片养分浓度存在显著差异，且凋落物状态与微位点均会影响分解速率。
在三种凋落物物种中，有两种的鲜叶凋落物分解速率快于衰老凋落物；且所有三种植物的凋落物在冠层间微位点的分解速率均快于冠层下微位点。本研究结果证实，动物产生并转运鲜叶凋落物是调控分解速率、以及植物生物质碳与养分向土壤转移过程的重要机制。