Affiliation(s)
1. The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 5290002, Israel
2. The School of Zoology, George S. Wise Faculty of Life Sciences, and The Steinhardt Museum of Natural History, Israel National Center for Biodiversity Studies, Tel Aviv University, Tel Aviv, 6997801, Israel
3. Key Laboratory for Restoration and Reconstruction of Degraded Ecosystem in Northwestern China of Ministry of Education, Ningxia University, Yinchuan 750021, China
ABSTRACT
Livestock grazing and trampling
is an important factor in the formation and development of different terrestrial
ecosystems. However, despite numerous studies on soil compaction, there is still
no consensus as to which kind of effect (positive or negative) animal trampling
exerts on soil nematodes. The main goal of this study was to evaluate the animal
trampling effect on free-living nematode abundance and diversity, and to define
the attenuating effect of the tree canopies (Cupressus sempervirens, Eucalyptus camaldulensis, and Tamarix aphylla) during wet and dry periods. The nematodes were extracted
from 100 g aliquots of soil samples (brown-red sandy soils) during cold-wet (CW),
warm-wet (WW), and hot-dry (HD) periods during 2013-2014, in a man-made safari-zoo
habitat, using the Baermann funnel procedure. Our results revealed the impact of trampling on both free-living nematode
abundance and diversity, and their soil habitat. It was found that trampling, along
with seasonal fluctuation and the tree-species attenuating effect on the soil medium,
resulted in the creation of the spatial-temporal heterogeneity of soil properties
in the study area. In turn, variation in soil properties was reflected in soil nematode
abundance and diversity, revealing tight correlation with the observed soil properties.
Animal trampling had an overwhelming, mostly negative impact on soil nematode abundance,
genera, and trophic diversity in the open, bare area. However, the protective effect
of the tree canopies, as well as seasonal fluctuations, attenuated this negative
impact. The trees had a significant attenuating effect on trampling compared with
the open, bare area. However, different tree species during the wet and dry periods
had a variable impact on nematode abundance, genera, and trophic diversity. During
the hottest period of the year, when external adverse factors dominated the trampling
effect, the ability of the trees to protect nematode communities was significantly
reduced. Of all the colonizer-persister (cp) continuum of nematode functional guilds, only
bacteria-feeding nematodes belonging to the cp-1 guild were positively affected by trampling. In general,
nematodes belonging to the r-life-strategy group (colonizers tolerant to environmental
disturbance), mainly bacteria-feeding nematodes, were the most numerous (61 and
44% at the trampling and undisturbed sites, respectively). In contrast to the bacteria-feeding
group, fungi-feeding nematodes were the smallest group in the study area (8 and
4% in the trampling and undisturbed sites, respectively). The undisturbed sites
were a more favorable habitat for the plant-parasite nematodes (9 and 26% in the
trampling and undisturbed sites, respectively). Surprisingly, the omnivore-predator
nematodes belonging to the K-life strategy group and that are characterized by hypersensitivity
to disturbance, were relatively numerous at the trampling (22%) and relatively undisturbed
(26%) sites. The results showed that 62%
of the nematode species were affected (48% negatively and 14% positively) by either
direct trampling or changes in soil properties. The ecological indices confirmed
that animal trampling had a negative impact on the soil biota in the study area. Our results suggested that
animal trampling exerts significant a direct and indirect effects (through changes in soil properties)
on soil free-living nematodes. Moreover, the wet-dry seasonal periods
along with the tree canopies protective effect may significantly change the extent
of animal trampling impact.
KEYWORDS
Grazing, soil disturbances, environmental
factors, biological indicators, ecological index.
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