Global Change Abstracts The Swiss Contribution - SCNAT

110
08.1-190
Rhizodeposition of C and N in peas and oats
after C-13-N-15 double labelling under field
conditions
Wichern F, Mayer J, Jörgensen R G, Müller T
Germany, Switzerland
Agriculture, Soil Sciences , Geochemistry & Geophysics
, Plant Sciences
Compounds released by plant roots during growth
can make up a high proportion of below-ground
plant (BGP) carbon and nitrogen, and therefore
influence soil organic matter turnover and plant
nutrient availability by stimulating the soil microorganisms.
The present study was conducted
to examine the amount and fate of C (CdfR) and N
rhizodeposits (NdfR), in this study defined as rootderived
C or N present in the soil after removal
of roots and root fragments, released during reproductive
growth. BGP biomass of peas (Pisum
satiumn L.) and oats (Avena sativa L.) was successfully
labelled in situ with a C-13-glucose (15) Nurea
mixture under field conditions using a stem
feeding method. Pea plants were labelled at the
beginning of flowering and harvested 36 and 52
days after labelling at pod filling (Pp) and maturity
(Pm), respectively. Oat plants were labelled
at grain filling and harvested 42 days after labelling
at maturity (O-M). CdfR was 24.2% (Pp), 29.6%
(Pm) and 30.8% (O-M) of total recovered plant C.
NdfR was 32.1% (Pp), 36.4% (Pm) and 30.0% (O-M)
of total plant N. Due to higher N assimilation,
amounts of NdfR were four times higher in peas
in comparison with oats. The results for NdfR in
peas were higher than results from other studies.
The C- to-N ratio of rhizodeposits was lower under
peas (17.3) than under oats (41.9) at maturity.
At maturity, microbial CdfR at 0 30cm soil depth
was 37% of the microbial biomass C in peas and
59% in oats. Microbial NdfR was 15% of microbial
N in peas and 5% in oats. Furthermore, inorganic
NdfR was 34% in peas and 9% in oats at 0-30cm at
maturity. These results show that rhizodeposits of
peas provide a more easily available substrate to
soil microorganisms, which are incorporated to a
greater extent and turned over faster in comparison
with oats. Beside the higher amounts of N released
from pea roots, this process contributes to
the higher N-availability for subsequent crops.
Soil Biology Biochemistry, 2007, V39, N10, OCT, pp
2527-2537.
08.1-191
Genetic rescue persists beyond first-generation
outbreeding in small populations of a rare
plant
Willi Y, van Kleunen M, Dietrich S, Fischer M
Global Change Abstracts – The Swiss Contribution | Terrestrial Ecosystems
Switzerland, Australia, South Africa, Germany
Biodiversity , Plant Sciences , Ecology
Habitat fragmentation commonly causes genetic
problems and reduced fitness when populations
become small. Stocking small populations with
individuals from other populations may enrich
genetic variation and alleviate inbreeding, but
such artificial gene flow is not commonly used
in conservation owing to potential outbreeding
depression. We addressed the role of long-term
population size, genetic distance between populations
and test environment for the performance of
two generations of offspring from between-population
crosses of the locally rare plant Ranunculus
reptans L. Interpopulation outbreeding positively
affected an aggregate measure of fitness, and the
fitness superiority of interpopulation hybrids was
maintained in the second offspring (F2) generation.
Small populations benefited more strongly
from interpopulation outbreeding. Genetic distance
between crossed populations in neutral
markers or quantitative characters was not important.
These results were consistent under
near-natural competition-free and competitive
conditions. We conclude that the benefits of interpopulation
outbreeding are likely to outweigh
potential drawbacks, especially for populations
that suffer from inbreeding.
Proceedings of the Royal Society B Biological Sciences,
2007, V274, N1623, SEP 22, pp 2357-2364.
08.1-192
Vegetation effects on pedogenetic forms of
Fe, Al and Si and on clay minerals in soils in
southern Switzerland and northern Italy
Zanelli R, Egli M, Mirabella A, Giaccai D, Abdelmoula
M
Switzerland, Italy, France
Agriculture, Soil Sciences , Geochemistry & Geophysics
, Ecology
The older forest type Quercetum-Bettiletum (oak/
birch; Q-type vegetation) in southern Switzerland
and northern Italy was to a large extent replaced
by chestnut forests (Castanea sativa; C-type vegetation)
in roman times. When laurophylloid vegetation
(L-type vegetation) invaded some of these
chestnut systems during the last few decades, it
caused detectable changes in organic chemistry.
The invasion of the L-type vegetation was predominately
due to increased winter temperatures. We
tested whether these vegetation changes led to
measurable long-term and short-term responses
of the mineral matrix by comparing soils under
Q-type with C-type vegetation (probing for longterm
effects; >100-2000 years) and soils under C-
type with L-type vegetation (short-term effects;