Net primary production (NPP) is influenced by disturbance-driven fluctuations in foliar standing crop (FSC) and resource-driven fluctuations in rates of recruitment and growth, yet most studies of NPP have focused primarily on factors influencing growth. We quantified NPP, FSC, recruitment, and growth rate for the giant kelp, Macrocystis pyrifera, at three kelp forests in southern California, U.S.A., over a 54-month period and determined the relative roles of FSC, recruitment, and growth rate in contributing to variation in annual NPP. Net primary production averaged between 0.42 and 2.38 kg dry mass x m(-2) x yr(-1) at the three sites. The initial FSC present at the beginning of the growth year and the recruitment of new plants during the year explained 63% and 21% of the interannual variation observed in NPP, respectively. The previous year's NPP and disturbance from waves collectively accounted for 80% of the interannual variation in initial FSC. No correlation was found between annual growth rate (i.e., the amount of new kelp mass produced per unit of existing kelp mass) and annual NPP (i.e., the amount of new kelp mass produced per unit area of ocean bottom), largely because annual growth rate was consistent compared to initial FSC and recruitment, which fluctuated greatly among years and sites. Although growth rate was a poor predictor of variation in annual NPP, it was principally responsible for the high mean values observed for NPP by Macrocystis. These high mean values reflected rapid growth (average of approximately 2% per day) of a relatively small standing crop (maximum annual mean = 444 g dry mass/m2) that replaced itself approximately seven times per year. Disturbance-driven variability in FSC may be generally important in explaining variation in NPP, yet it is rarely examined because cycles of disturbance and recovery occur over timescales of decades or more in many systems. Considerable insight into how variation in FSC drives variation in NPP may be gained by studying systems such as giant kelp forests that are characterized by frequent disturbance and rapid rates of growth and recruitment.

译文

净初级生产 (NPP) 受干扰驱动的叶面作物 (FSC) 波动和资源驱动的招聘和增长速度波动的影响,但对NPP的大多数研究主要集中在影响增长的因素上。我们在54个月的时间内对美国南加州的三个海带森林中的巨型海带Macrocystis pyrifera的NPP,FSC,招募和增长率进行了量化,并确定了FSC,招募,和增长率对年度NPP变化的贡献。在这三个地点,净初级产量平均在0.42和2.38千克干重x m(-2) x yr(-1) 之间。最初的FSC出现在生长年的开始以及该年新植物的招募分别解释了NPP中观察到的年际变化的63% 和21%。前一年的NPP和波浪干扰共同占初始FSC年际变化的80%。没有发现年增长率 (即单位现有海带质量产生的新海带质量) 与年NPP (即单位海底面积产生的新海带质量) 之间的相关性,主要是因为与最初的FSC和招聘相比,年增长率是一致的,后者在年份和地点之间波动很大。尽管增长率不能很好地预测年度NPP的变化,但它主要是导致大囊藻观察到NPP的高平均值的原因。这些高平均值反映了相对较小的立地作物 (最大年平均值 = 444克干重/平方米) 的快速生长 (平均约每天2%),该作物每年约替代自身7次。FSC中的扰动驱动的变异性通常对于解释NPP的变化很重要,但是很少进行检查,因为在许多系统中,扰动和恢复的周期会在几十年或更长时间的时间范围内发生。通过研究以频繁干扰以及快速生长和招募速度为特征的巨型海带森林等系统,可以对FSC的变化如何驱动NPP的变化有相当大的了解。

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