Maurer Deborah A, Zedler Joy B
Botany Department, University of Wisconsin-Madison, 430 Lincoln Drive, Madison, WI, 53706-1381, USA.
Oecologia. 2002 Apr;131(2):279-288. doi: 10.1007/s00442-002-0886-8. Epub 2002 Apr 1.
Phalaris arundinacea (Poaceae) is aggressively invading wetlands across North America. We tested the hypotheses that open canopies and increased nutrients facilitate vegetative establishment in the field, using a phytometer (6 rhizome fragments/plot, 24 plots/wetland). In each of three wetlands, phytometers received three levels of an NPK fertilizer or served as controls. Emergence and survival differed among sites (P=0.0005), but not due to NPK addition. P. arundinacea survival was highest in a wet prairie with a late-developing canopy, but limited by prolonged flooding in one sedge meadow and by an early-growing, dense plant canopy in a second. These patterns were explained in greenhouse experiments, where both flooding (P<0.0001) and heavy shade (P=0.0002) decreased P. arundinacea aboveground biomass by up to 73% and 97%, respectively. Rhizome fragment survival was reduced by 30% under flooded conditions and 25% under heavy shade. We then tested the hypothesis that a clonal subsidy facilitates vegetative expansion into heavy shade. Established clones were allowed access to bare soil under four levels of shade and two levels of NPK fertilizer in a two-factor greenhouse experiment. Young ramets attached to parent clones readily grew into heavy shade, and the high nutrient treatment increased aboveground growth (P<0.0001) and distance of ramet spread (P=0.0051) by nearly 50%. Under low nutrient conditions, root biomass increased by 30% (P<0.0001). P. arundinacea's rapid expansion into a variety of wetland types is likely a function of clonal subsidy, morphological plasticity, and nutrient availability: young ramets that emerge under shaded conditions are supported by parental subsidies; where nutrients are plentiful, P. arundinacea can maximize aboveground growth to capture more light; and where nutrients are scarce, it can increase belowground foraging.
虉草（禾本科）正在北美洲大肆入侵湿地。我们使用植物测定法（每块样地6个根茎片段，每个湿地24块样地）检验了以下假设：开阔的冠层和增加的养分有利于该植物在野外进行营养繁殖。在三个湿地中，每个湿地的植物测定法样本分别接受三种水平的氮磷钾肥料处理或作为对照。不同地点的出苗率和存活率存在差异（P = 0.0005），但并非由于添加氮磷钾肥料所致。虉草在冠层发育较晚的湿草原中存活率最高，但在一个莎草草甸中受到长时间洪水的限制，在另一个湿地中则受到早期生长且茂密的植物冠层的限制。这些模式在温室实验中得到了解释，在该实验中，洪水（P < 0.0001）和重度遮荫（P = 0.0002）分别使虉草的地上生物量减少了高达73%和97%。在水淹条件下，根茎片段的存活率降低了30%，在重度遮荫条件下降低了25%。然后，我们检验了以下假设：克隆补贴有利于虉草在重度遮荫环境中进行营养繁殖扩张。在一项双因素温室实验中，使已建立的克隆体在四种遮荫水平和两种氮磷钾肥料水平下接触裸露土壤。附着在亲本克隆体上的幼分株很容易在重度遮荫环境中生长，高养分处理使地上生长量（P < 0.00）和分株扩散距离（P = 0.0051）增加了近50%。在低养分条件下，根系生物量增加了30%（P < 0.0001）。虉草能够迅速扩展到各种湿地类型，这可能是克隆补贴、形态可塑性和养分有效性共同作用的结果：在遮荫条件下出现的幼分株得到亲本补贴的支持；在养分充足的地方，虉草可以最大化地上生长以获取更多光照；而在养分稀缺的地方，它可以增加地下觅食能力。
