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TEMPORAL VARIABILITY MATTERS: EFFECTS OF CONSTANT VS. VARYING MOISTURE AND SALINITY ON GERMINATION
Author(s) -
Noe Gregory B.
Publication year - 2002
Publication title -
ecological monographs
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.254
H-Index - 156
eISSN - 1557-7015
pISSN - 0012-9615
DOI - 10.1890/0012-9615(2002)072[0427:tvmeoc]2.0.co;2
Subject(s) - germination , salinity , moisture , microcosm , water content , biology , ecology , agronomy , environmental science , horticulture , chemistry , geology , geotechnical engineering , organic chemistry
Most ecological experiments test constant environmental conditions instead of the temporally varying conditions that are typical of most ecological systems. This study experimentally evaluated the effects of temporal variations of soil salinity and moisture on the germination of an 11‐species annual plant assemblage. In soil‐based microcosms with common seed banks, constant conditions were compared to different amplitudes, durations, and seasonal timing of low salinity or high moisture that simulate conditions in the upper intertidal marsh of southern California during periods of germination. The percentage germination of seeds of eight species decreased when low salinity or high moisture lasted for 1 wk before changing to high salinity and low moisture for 3 wk (varying conditions) compared to 4 wk of low salinity or high moisture (constant conditions). The seed germination speed of two species differed (both faster and slower) between the varying and constant treatments. Species responses to varying vs. constant conditions depended on the specific amplitude of temporary low salinity (0, 8, or 17 g/kg) in the varying treatments. Similarly, the duration (1, 2, or 4 wk) of low salinity or high moisture affected the percentage germination (four species) and germination speed (two species). Percentage germination (four species) and germination speed (eight species) also differed according to whether low salinity and high moisture were initiated in November, January, or March. The sensitivity of species seeds to temporally varying conditions could be explained by their germination traits and identity as native or exotic. Seeds of the six exotic species were less sensitive to varying conditions, germinated faster, and were more tolerant of high salinity and low moisture than seeds of the five native species. Varying conditions resulted in different patterns of germination than constant conditions, and environmental factors typically vary through time in the field. Thus, experimenters who are trying to understand or predict plant establishment should consider and simulate, as closely as possible, the variability in field conditions.